Editing IPCC:AR6/WGII/Chapter-6 (section)

== 6.3 Adaptation Pathways ==

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=== 6.3.1 Introduction ===

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Adaptation pathways are composed of sequences of adaptation actions connected through collaborative learning with the possibility of enabling transformations in urban and infrastructure systems (Werners et al., 2021). Individual adaptation actions co-evolve with risks (see [[#6.2|Section 6.2]] ) and development processes ( [[#6.4|Section 6.4]] ) to compose more or less planned adaptation pathways that can include a range of unanticipated outcomes. This section engages with this complexity by approaching adaptation through the notion of infrastructure. The adaptation options for individual infrastructure systems are reviewed, and in [[#6.4|Section 6.4]] brought together through assessment of cross-cutting enabling conditions. Interpreted broadly, infrastructure includes the social systems, ecological systems and grey/physical systems that underpin safe, satisfying and productive life in the city and beyond (Grimm et al., 2016). Social infrastructure includes housing, health, education, livelihoods and social safety nets, cultural heritage/institutions, disaster risk management and security and urban planning. Ecological infrastructure includes nature-based services: temperature regulation, flood protection and urban agriculture. Grey, or physical infrastructure, includes energy, transport, water and sanitation, communications (digital), built form and solid waste management. Framing infrastructure in this way enables an assessment of adaptation that is not constrained to the administrative boundaries of urban settlements, but also includes the flows of material, people and money between urban, peri-urban and more rural places, and can include adaptation actions deployed by government, individuals and the private sector. Recognising the complexity of adaptation and the research literature that reaches beyond individual infrastructural domains, the section also reviews urban adaptation through the cross-cutting lenses of equity and mitigation. [[#6.4|Section 6.4]] assesses the enabling environment (political will, governance, knowledge, finance and social context) that shapes specific adaptation contexts and futures.

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=== 6.3.2 The Adaptation Gap in Cities and Settlements ===

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The adaptation gap is the difference between the ability to manage risk and loss and experienced risk and loss (Chen et al., 2016; [[#UNEP--2021|UNEP, 2021]] ). It describes both levels of capacity and residual risk. Figure 6.4 presents an analysis by IPCC World Region for urban populations and current levels for risk and loss. The analysis seeks to draw out equity considerations by comparing the poorest and wealthiest quintiles for each region and for adaptation to the direct impacts of flooding and heatwave, as well as impacts felt in cities that include climate change impacts on supply chains; water and food security. Figure 6.4 should not be used to compare regions but can be used to contrast adaptation gaps by hazard type within regions.

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[[File:700174251ccb7e743dc8b8066b71ff4f IPCC_AR6_WGII_Figure_6_004.png]]

'''Figure 6.4 |''' '''The Urban Adaptation Gap.''' This is a qualitative assessment presenting individual, non-comparative data for world regions from 25 AR6 Coordinating Lead Authors (CLAs) and Lead Authors (LAs), the majority from regional chapters. Respondents were asked to make expert summary statements based on the data included within their chapters and across the AR6 report augmented by their expert knowledge. Multiple iterations allowed opportunity for individual and group judgement. Urban populations and risks are very diverse within regions making the presented results indicative only. Variability in data coverage leads to the overall analysis having ''medium agreement'' , ''medium evidence'' . Major trends identified in 6.3.1 at least meet this level of confidence. Analysis is presented for current observed climate change associated hazards and for three adaptation scenarios: (1) current adaptation (based on current levels of risk management and climate adaptation), (2) planned adaptation (assessing the level of adaptation that could be realised if all national, city and neighbourhood plans and policies were fully enacted), (3) transformative adaptation (if all possible adaptation measures were to be enacted). Assessments were made for the lowest and highest quintile by income. Residual risk levels achieved for each income class under each adaptation scenario are indicated by five adaptation levels: no risk, occasional discomfort, occasional impacts on well-being, frequent impacts on well-being, extreme events and/or chronic risk. The urban adaptation gap is revealed when levels of achieved adaptation fall short of delivering ‘no risk’. The graphic uses IPCC Regions, and has split Asia into two regions: North and East Asia, and Central and South Asia. Technical support is acknowledged from Greg Dodds and Sophie Wang

The key finding from Figure 6.4 is that for all urban populations, both ''currently deployed'' and ''currently planned'' adaptations are not able to meet current levels of risk associated with climate change. Even if ''all conceivabl'' e adaptation was to be deployed, the majority of risks faced by the urban rich and poor today would not be fully resolved. This clearly emphasizes the fundamental importance of climate change mitigation to avoid urban risk and loss.

The urban adaptation gap is also found to be unequal. The poorest quintile has a larger adaptation gap than the richest quintile. Reported inequality in the application of urban adaptation is greatest in North, East and Southeast Asia, reflecting rapid urbanisation in this region. Reported inequality is lowest in Europe and Australasia. Observed inequalities indicate that the markets, government actions and civil society investments available to reduce vulnerability and risk among the poor have not been observed to offset inequalities based on individual and household capacities.

There is some catch-up as analysis moves through ''actually deployed'' to ''planned'' and ''all conceivable'' deployment, particularly for water and food security, but even here, inequality in risk is not fully resolved. Africa and South and Central Asia in particular show considerable disparity in adaptation to urban food security even with ''all conceivable adaptation'' . This means that even if all available adaptation was to be deployed, inequality in ability to adapt to climate change would remain. This highlights the significance of addressing underlying inequalities in development that shape differential vulnerability (see [[#6.2.3.1|Section 6.2.3.1]] , 6.2.3.3, 6.3.5.1 and 6.4) as part of vision and action on reducing risk to climate change so that no one is left behind.

Some hazard types and regions show strong capacity to close the adaptation gap if ''all planned'' adaptation was to be deployed: for example, Europe for heatwave and Europe and Central and South America for riverine and coastal flooding (particularly for wealthier populations). This reveals capacity within the current approaches to climate risk management, but also highlights the importance of resolving challenges that prevent planned adaptation from being deployed and deployed equitably.

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=== 6.3.3 Adaptation Through Social Infrastructure ===

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Social infrastructure refers to social, cultural and financial activities and institutions as well as associated property, buildings and artefacts that can be deployed to reduce risk and recover from loss. This section examines land use planning, livelihoods and social protection, emergency and disaster risk management, health systems, education and communication, and cultural heritage.

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==== 6.3.3.1 Land Use Planning ====

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Land use planning plays a major role in the siting of settlements and infrastructure. In relation to climate change, it affects whether development takes place in locations that are exposed to hazards; similarly, it shapes the potential effects that the built environment can have on natural systems. Despite this, generally speaking, there is limited implementation of zoning and land use measures for climate adaptation from cities across diverse contexts ( ''robust evidence'' , ''high agreement'' ), see for example Maputo ( [[#Castán%20Broto--2014|Castán Broto, 2014]] ), sub-Saharan cities (Dodman et al., 2017) and Amman, Moscow and Delhi ( [[#Jabareen--2015|Jabareen, 2015]] ). Certain countries, such as South Korea, have, however, recently begun to address disaster risk reduction within their land use planning systems (Han et al., 2019).

Conventional zoning regulations (in which only one kind of use is permitted in a given area) and land use planning range in scale from the regional to the local and can be deployed to minimise risks through protection, accommodation or retreat. Protection entails, in addition to allocating zones for protective urban infrastructure (such as seawalls, levees and dykes, and slope revetments), avoidance measures that restrict or prevent urban development (e.g., through growth containment and/or no-build zones). Accommodation involves land use modifications and/or conversions while retreat requires either compulsory or voluntary relocations and may entail buyouts (Butler, Deyle and Mutnansky, 2016; [[#León--2016|León and March, 2016]] ; Lyles, Berke and Overstreet, 2018). Risk eliminating retreat measures are less widely adopted than other risk reducing zoning and land use measures (Anguelovski et al., 2016; Butler, Deyle and Mutnansky, 2016; Lyles, Berke and Overstreet, 2018). This is attributed to the controversies of relocation and to the complexities of buyouts (Butler, Deyle and Mutnansky, 2016; King et al., 2016).

Evidence from both richer countries and the Global South reveals that conventional zoning is more effective when governance systems facilitate the implementation of land use policies for climate adaptation that preclude negative human-nature interactions and that curb spatial inequity, both of which can trigger climate gentrification and increase the vulnerability of economically disadvantaged groups to climate-related risk ( ''high confidence'' ) ( [[#Marks--2015|Marks, 2015]] ; Liotta et al., 2020; Keenan, Hill and Gumber, 2018). Cascading benefits of zoning and land use planning for climate adaptation are associated with the use of soft land cover, green infrastructure and improvement of livability through better conditions for walkability and cycling. This decreases auto-dependency and contributes to health and economic development (by attracting businesses and retail that stimulate economic prosperity and increase property values) ( [[#Larsen--2015|Larsen, 2015]] ; Carter et al., 2015). Such increases in property values have also been observed in zones and areas protected from risks (such as flooding), where it may trigger spatial inequity leading to climate gentrification ( [[#Marks--2015|Marks, 2015]] ; [[#Votsis--2017|Votsis, 2017]] ; [[#Votsis--2016|Votsis and Perrels, 2016]] ; Keenan, Hill and Gumber, 2018).

Adaptation actions through zoning and land use are more effective when combined with other planning measures ( ''high confidence'' ), for example with ecosystem-based adaptations (e.g., for flood management and curbing the urban heat island effect) ( [[#Larsen--2015|Larsen, 2015]] ; [[#Nalau--2018|Nalau and Becken, 2018]] ; [[#Perera--2018|Perera and Emmanuel, 2018]] ; Anguelovski et al., 2016; Carter et al., 2015; Tsuda and Duarte, 2018; [[#Nolon--2016|Nolon, 2016]] ); with community-based adaptations (trade-offs and valuations, i.e., which land uses are valued more) ( [[#Larsen--2015|Larsen, 2015]] ; [[#Nalau--2018|Nalau and Becken, 2018]] ; [[#Perera--2018|Perera and Emmanuel, 2018]] ; Anguelovski et al., 2016; Carter et al., 2015; McPhearson et al., 2018; [[#Nolon--2016|Nolon, 2016]] ); and with built form regulations and codes ( [[#León--2016|León and March, 2016]] ; [[#Yiannakou--2017|Yiannakou and Salata, 2017]] ; [[#Perera--2018|Perera and Emmanuel, 2018]] ; [[#Straka--2019|Straka and Sodoudi, 2019]] ; [[#Larsen--2015|Larsen, 2015]] ; [[#Nolon--2016|Nolon, 2016]] ). The imposition of planning-based tools such as scenario planning, flexible zoning and development incentivisation (among others) has the capacity to influence and encourage these adaptations (United States Environmental Protection Agency, 2017). Local risk-reduction inputs can inform land use adaptation policies (accommodation and/or avoidance, specifically growth containment and no-build zones) that are better integrated within larger urban plans (Lyles, Berke and Overstreet, 2018; [[#Nalau--2018|Nalau and Becken, 2018]] ; Tsuda and Duarte, 2018) ( ''limited evidence'' , ''high agreement'' ).

Implementation of zoning and land use measures for climate adaptation from cities across diverse contexts remains limited ( ''high agreement'' , ''robust evidence'' ) owing to a range of challenges. A range of evidence from multiple locations indicates the challenges of mainstreaming land use planning for climate adaptation, including in Bangkok, Thailand ( [[#Marks--2015|Marks, 2015]] ), Legazpi City and Camalig Municipality in the Philippines (Cuevas et al., 2016; [[#Cuevas--2016|Cuevas, 2016]] ), the USA (Cuevas et al., 2016; [[#Cuevas--2016|Cuevas, 2016]] ), British Columbia, Canada ( [[#Stevens--2017|Stevens and Senbel, 2017]] ), and Australia (Serrao-Neumann et al., 2017). Mainstreaming is hindered by a lack of clarity of implementation strategies for climate adaptation, insufficient funding, competing priorities (especially among professional planners and politicians), institutional challenges (see Jabareen’s [2015] study of 20 cities globally) and the need to fill data gaps and continuously update weather statistics ( [[#Oberlack--2018|Oberlack and Eisenack, 2018]] ) ( ''medium evidence'' , ''high agreement'' ). At the same time, however, limited evidence from cities around the world such as the urban regions of Stuttgart and Berlin in Germany ( [[#Larsen--2015|Larsen, 2015]] ), Greater Manchester in the UK (Carter et al., 2015), and Colombo in Sri Lanka ( [[#Perera--2018|Perera and Emmanuel, 2018]] ) reveals that risk reduction through zoning and land use can effectively protect and expand green infrastructure and soft land cover to alleviate pluvial flooding and decrease the urban heat island effect. This evidence points that one of the primary roles of land use planning is to guide the development of the urban form. As such, it underpins and establishes the basis for other infrastructure systems such as physical infrastructure and nature-based solutions (Morrissey, Moloney and Moore, 2018).

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==== 6.3.3.2 Livelihoods and Social Protection ====

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Understanding how livelihoods, particularly of the urban poor, are both impacted by climate risk and how they might be strengthened is central to understanding climate adaptation in cities and settlements (Dobson et al. 2015). Rapid urbanisation and expanding physical infrastructure do not have a clear relationship with improved outcomes for urban livelihoods of low-income residents (Soltesova et al., 2014). Municipal and national efforts need to be closely aligned with building adaptive capacity of residents themselves, often through community-based adaptation (Soltesova et al., 2014; Dobson, Nyamweru and Dodman, 2015). Social safety nets protect individuals or households from falling below a defined standard of living by providing cash, in kind and other social transfers to fight vulnerabilities ( [[#Islam--2019|Islam and Hasan, 2019]] ) including those associated with climate change impacts including food shocks. Strengthening the financial and social infrastructure of poor households is a critical component of adaptive and transformative capacity (Haque, Dodman and Hossain, 2014; Ziervogel, Cowen and Ziniades, 2016). Social safety nets are one mechanism for strengthening this capacity.

Social protection, or social security, is defined as the set of policies and programmes designed to reduce and prevent poverty and vulnerability throughout the lifecycle ( [[#ILO--2017|ILO, 2017]] ). Safety nets are intended to protect vulnerable households from impacts of economic shocks, natural hazards and disasters, and other crises. The UN policy frameworks for sustainable development, including the Sendai Framework for Disaster Risk Reduction 2015–2030, the new Strategic Framework 2018–2030 of the United Nations Convention to Combat Desertification (UNCCD) and UNFCCC, highlight the essential role of social protection in promoting comprehensive risk management ( [[#Aleksandrova--2019|Aleksandrova, 2019]] ). Since the term Adaptive Aocial Protection was introduced by the [[#World%20Bank--2015|World Bank (2015)]] and the [[#IPCC--2014|IPCC (2014)]] , it has been an emerging strategic tool to integrate poverty reduction, disaster risk reduction and humanitarian development into adaptation to climate change (Béné, Cornelius and Howland, 2018; [[#Aleksandrova--2019|Aleksandrova, 2019]] ; Watson et al., 2016).

Adaptive social protection (ASP) is defined as a resilience-building approach by combining elements of social protection, disaster risk reduction and climate change adaptation, so as to break the cycle of poverty and vulnerability of household by investing in their capacity to prepare for, cope with and adapt to all types of shocks, especially under climate change and other global challenges (Bowen et al., 2020; Ivaschenko et al., 2018). ASP has been justified as an effective instrument to build household and community resilience to climate extremes and slow-onset climate events such as sea level rise and environmental degradation ( [[#Schwan--2018|Schwan and Yu, 2018]] ; [[#Aleksandrova--2019|Aleksandrova, 2019]] ). In contexts of extreme poverty or climatic extremes, international development organisations, national provisions and market charities are complementary where family and kinship networks are weak and inadequate. To deal with short-term vulnerability to climate shocks, ASP can act as a crucial complement to risk management tools provided by communities and markets, tools which tend to be insufficient in the face of large or systemic shocks, by providing predictable transfers, developing human capital and diversifying livelihoods (Hallegatte et al., 2016). ASP can also facilitate long-term change and adaptation by improving education and health levels, as well as providing a proactive approach to managing climate-induced migration in both rural and urban areas ( [[#Schwan--2018|Schwan and Yu, 2018]] ; Adger et al., 2014).

Many national ASP programmes are established to cover both rural and urban areas, however, only a small number of researchers pay attention to urban cases ( [[#Aleksandrova--2019|Aleksandrova, 2019]] ). ASP instruments can be classified into four major types as presented in Table 6.5 (Ivaschenko et al., 2018; [[#ILO--2017|ILO, 2017]] ). ASP can contribute to both incremental and transformative interventions both at the system level (short-term and long-term coping strategies from communities) and at the beneficiaries’ level (vulnerable populations) (Béné, Cornelius and Howland, 2018; [[#World%20Bank--2015|World Bank, 2015]] ; [[#Aleksandrova--2019|Aleksandrova, 2019]] ; Ivaschenko et al., 2018).

'''Table 6.5 |''' Four categories and examples of adaptive social protection.

{| class="wikitable"
|-
! '''Category'''

! '''Example'''

! '''Urban cases'''

! '''Function'''

|-
| Social safety nets (or social assistance)

| Conditional and unconditional cash transfers, including non-contributory pensions and disability, birth and death allowances;

Food stamps, rations, emergency food distribution, school feeding and subsidies;

Cash or food for work programmes;

Free or subsidised health services;

Housing and utility subsidies;

Scholarships and fee waivers, etc.

| * A targeted asset transfer project for urban extreme poor in Dhaka city ( [[#Hossain--2018|Hossain and Rahman, 2018]] )
* Emergency food stockpiling in Japan; safety net food stocks in India, Indonesia and Malaysia (Lassa et al., 2019)
* Household cash transfer programme in contingency planning in Mexico (Ivaschenko et al., 2018)
* Governmental transfer to hurricane affected households in USA (Bowen et al., 2020)
* Non-contributory disability cash benefits ( [[#ILO--2017|ILO, 2017]] )

| Incremental adaptation; protective measures

|-
| Social insurance

| Old age, survivor and disability contributory pensions;

Occupational injury benefit, sick or maternity leave;

Health insurance, etc.

| Old-age social pensions (Ivaschenko et al., 2018)

| Incremental adaptation and ''ex ante'' prevention

|-
| Labour market policies

| Unemployment, severance and early retirement compensation;

Training, job sharing and labour market services;

Wage subsidises and other employment incentives, including for disabled people, etc.

| Public works and employment protection in Africa, Asia cases ( [[#World%20Bank--2015|World Bank, 2015]] ; [[#ILO--2017|ILO, 2017]] ; Ivaschenko et al., 2018)

| ''Ex post'' protection and ''ex ante'' prevention measures, incremental adaptation

|-
| Livelihood development measures

| Income diversification, employment support, weather-index insurance, housing subsidies, post-disaster construction, relocation planning, livelihood shift strategies, etc.

| Multiple programmes for differing household needs in Philippines (Bowen et al., 2020);

Weather-index insurance in Chinese coastal cities ( [[#Rao--2019|Rao and Li, 2019]] );

Early warning forecast system and public meteorological service information in Beijing (Song, Zheng and Lin, 2021)

| Promotive and anticipatory measures; transformational adaptation

|}

ASP may be very good at reducing extreme poverty by helping to meet individual or household needs but not collective needs to mitigate long-term climate shocks. For example, few programmes consider risk assessment and climate-proof infrastructures as anticipatory measures to foster early action and preparedness ( [[#Aleksandrova--2019|Aleksandrova, 2019]] ; Costella et al., 2017). They therefore need to enable the adoption of forward-looking strategies for long-lasting adaptation ( [[#Tenzing--2020|Tenzing, 2020]] ). Some examples from China show social protection can improve adaptive capacity of urban communities with social medical insurance, housing subsidies, weather-index insurance, post-disaster construction, relocation planning, livelihood shift strategies, and so on. (Pan et al., 2015; Zheng et al., 2018b; [[#Rao--2019|Rao and Li, 2019]] ; Song, Zheng and Lin, 2021). However, social protection may lead to maladaptation in urban policy when social security, or similar tools (for example insurance) to compensate for exposure deincentivise risk reduction ( [[#Grove--2021|Grove, 2021]] ). In many developing countries, high concentrations of poor and vulnerable groups living in disaster-prone zones of urban centres, new urban dwellers and informal residents are often excluded from community-based networks and social services ( [[#Aleksandrova--2019|Aleksandrova, 2019]] ). Risk transfer tools (such as insurance) and risk retention measures (such as social safety nets) can avoid and minimise the burden of loss and damage and limit secondary and indirect effects ( [[#Aleksandrova--2019|Aleksandrova, 2019]] ; [[#Roberts--2018|Roberts and Pelling, 2018]] ).

Inclusive, targeted, responsive and equitable social protection can support long-term transition toward more sustainable, adaptive and resilient societies (Hallegatte et al., 2016; Shi et al., 2018; Béné, Cornelius and Howland, 2018; [[#Carter--2018|Carter and Janzen, 2018]] ; Adger et al., 2014). ASP systems can be cost effective and equitable when targeting accuracy, timely risk sharing (disaster assistance) and improved policy coherence. [[#Carter--2018|Carter and Janzen (2018)]] find that the long-term level and depth of poverty can be improved by incorporating vulnerability targeted social protection into a conventional social protection system. Countries at all income levels can set up ASP systems that increase resilience to natural hazards, but the systems need to identify cost–benefits and be scalable and flexible to adjust to future, increasing climate risk. [[#Bastagli--2014|Bastagli (2014)]] suggested a new design for effective social protection including: (i) increasing the amount or value of transfer; (ii) extending the coverage of beneficiaries; and (iii) introducing payments or new programmes of social protections. For social protection programmes to contribute more effectively to adaptation, they need to be better coordinated across a range of agencies; better integrated with climate data to anticipate times of need for vulnerable groups; and better aligned with other risk management instruments such as insurance (Agrawal et al., 2019).

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==== 6.3.3.3 Emergency and Disaster Risk Management ====

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There is growing evidence of the benefits of early warning systems for urban preparedness decision making and action for climate and weather-related hazards such as cyclones, hurricanes and floods ( ''medium evidence'' ; ''high agreement'' ) (Lumbroso, Brown and Ranger, 2016; [[#Zia--2015|Zia and Wagner, 2015]] ; Marchezini et al., 2017). Climate forecasting is constantly evolving and becoming increasingly accurate. Global organisations such as the World Meteorological Organizations are increasingly focusing on new and emerging technologies such as crowdsourced data collection to support integrated city services and early warning systems (Baklanov et al., 2018). However, while climate forecasting is an increasingly central tool for risk management agencies, a focus on urban areas or key infrastructure is still considerably rare (Lourenço et al., 2015; Nissan et al., 2019; Harvey et al., 2019). The significant rise in urban risks poses significant challenges to humanitarian agencies. Humanitarian responses and local emergency management are vital for disaster risk reduction yet are compromised in urban contexts where it is difficult to confirm property ownership and where renters and informal dwellers are often excluded from decision-making and planning ( [[#Parker--2015|Parker and Maynard, 2015]] ; Maynard et al., 2017). Disaster survivors and growing urban refugee populations are often displaced across the city thereby complicating efforts to track and provide support (Maynard et al., 2017).

Existing early warning systems remain insufficient and the complexity of urban landforms makes accurate and detailed early warning difficult ( ''medium evidence'' ; ''high agreement'' ) (Jones et al., 2015). This is particularly the case in low- and middle-income countries (LMICs) where urban centres are often characterised by rapid expansion of interlinked formal and informal human settlements and land use zones. In such contexts, early warning services vary in effectiveness within the same urban centre (Allen et al., 2020c; Rangwala et al., 2018). Often, forecast-based action follows linear structures where forecast information is applied mainly for responding to negative impacts rather than anticipatory decision-making and preparation to avoid such impacts (Marchezini et al., 2017). Early warning systems are effective for warning of threshold breaching events including cyclonic activity and riverine flooding but less able to provide localised warning, though capability is rapidly increasing. Probabilistic risk forecasting and forecast based early action are only beginning to be applied to urban contexts and often those that are most vulnerable do not receive warnings regarding hazardous events (Nissan et al., 2019). There is less capacity for early warning systems in LMICs with key challenges linked to a lack of well-established risk baseline information; accessibility, communication and understanding of forecast information, as well as political and institutional barriers and limited resources and capacities to act on such information (Jones et al., 2015; Mustafa et al., 2015; [[#Zia--2015|Zia and Wagner, 2015]] ; Marchezini et al., 2017; Gotgelf, Roggero and Eisenack, 2020). Political and institutional barriers to the incorporation of climate information to decision-making are not limited to LMICs (Harvey et al., 2019). For example, comprehensive studies on sectoral use of climate information in Europe revealed that, despite climate services becoming increasingly accessible and well resourced, there is limited organisational uptake of seasonal climate forecasts across key sectors (e.g., energy, transport, water and infrastructure) in informing their decision making processes ( [[#Soares--2016|Soares and Dessai, 2016]] ; Soares, Alexander and Dessai, 2018). This is due both to technical and non-technical barriers such as lack of awareness and knowledge of climate information and forecasting ( [[#Soares--2016|Soares and Dessai, 2016]] ; Soares, Alexander and Dessai, 2018).

Globally, a considerable diversity of tools and frameworks for urban resilience assessments are being developed at multiple scales ( [[#Arup%20and%20Rockefeller--2015|Arup and Rockefeller, 2015]] ; Elias-Trostmann et al., 2018). These include hybrids such as ecosystem-based disaster risk reduction (Eco-DRR) (Begum et al., 2014).While important advances have been made in assessing urban resilience, much debate remains around such tools and assessment approaches regarding issues such as validation, dynamics in exposure and vulnerability, and appropriateness of generic methods in high-density urban settlements (Leitner et al., 2018; Cardoso et al., 2020; Rufat et al., 2019). Disaster impact and recovery time are strongly influenced by the behaviour and actions of individuals, communities, businesses, and government organisations ( [[#Meriläinen--2020|Meriläinen, 2020]] ; Räsänen et al., 2020). For example, the review by Aaerts et al. (2018) shows how the limitations of existing flood risk assessment methods (which tend to account for human behaviour in limited terms) can be addressed through innovative flood-risk assessments that integrate behavioural adaptation dynamics. The study by [[#Moghadas--2019|Moghadas et al. (2019)]] highlights the importance of hybrid multi-criteria approaches for assessing urban flood resilience in Tehran, Iran. A growing literature shows how multidisciplinary and inclusive approaches that include Local knowledge can achieve greater accuracy in risk characterisation and support lasting impact of investments into more robust climate services (Aerts et al., 2018; Lourenço et al., 2015; Sword-Daniels et al., 2018; Singh et al., 2018; Nissan et al., 2019; Harvey et al., 2019; [[#Simon--2020|Simon and Palmer, 2020]] ). This literature highlights the need for innovative approaches in urban contexts that transcend traditional approaches of local knowledge inclusion widely applied in rural contexts, such as participatory rural appraisal.

The inclusion of Local knowledge and Indigenous knowledge in urban vulnerability and risk assessments can strongly enhance local resilience, but its effectiveness is constrained by wider decision making and policy contexts dominated by top-down approaches ( ''medium evidence'' ; ''high agreement'' ) (Jones et al., 2015; Sword-Daniels et al., 2018; Nissan et al., 2019). Established non-state actors such as Shack and Slum Dwellers International are particularly effective at implementing inclusive approaches for local knowledge incorporation into urban decision-making. Climate change and disaster risk exacerbate existing problems of economic development, yet macro-economic planning seldom incorporates adaptation. Recent evidence also confirms the role of Indigenous knowledge and local knowledge in management practices to reduce climate risks through early warning preparedness and response (see also [[#6.3.2|Section 6.3.2.3]] ). These practices are particularly important where alternative early warning methods are absent. For instance, Abudu Kasei et al. (2019) show that Indigenous knowledge gathered through observations on changes in natural indicators (such as links between rainfall patterns, certain flora and fauna, and temperature changes) could be applied to develop early warning of climate hazards (floods and droughts) in informal urban settlements in African countries such as Ghana. Similarly, Hiwaski et al. (2015) show that observations of changes in the environment and celestial bodies are used to predict climate-related hazards in Indonesia, the Philippines and Timor-Leste where communities in turn use local materials and methods, and customary practices to respond to the impacts of climate change.

Insurance is a risk transfer mechanism for middle- and high-income countries, yet is less widely available in LMICs ( [[#Surminski--2017|Surminski and Thieken, 2017]] ). Additionally, where insurance options do exist in LMICs, these are not usually available to large populations living or operating in the informal sector. Flood insurance is widely available in many Organisation for Economic Co-operation and Development (OECD) countries but the demand and uptake differ significantly across countries (Hanger et al., 2018). This financial tool is subject to increasing pressure under the changing climate, with growing concerns around affordability and availability. More integrative approaches are required, such as where changes in the insurance industry are closely linked to adaptation strategies, building standards and land use planning and their application (Cremades et al., 2018). This is particularly important in LMICs and of central concern for all insurance schemes is ensuring access, fairness and affordability for the most poor and vulnerable. However, there are some notable examples of low-income communities setting up their own disaster insurance mechanisms. For example, the Community Development Funds for the Baan Mankong upgrading programme in Thailand include disaster funds as insurance against housing damage ( [[#Archer--2012|Archer, 2012]] ). Such approaches also need to be more closely linked to existing urban risk management planning approaches where urban livelihoods are seldom integrated and informed by more dynamic risk reduction frameworks that consider adaptive cycles and how resilience changes over time ( [[#Beringer--2018|Beringer and Kaewsuk, 2018]] ; Cremades et al., 2018).

Disaster risk management systems face increasing challenges in adapting to evolving risk profiles, shaped by expanding urban areas and changing environmental conditions associated with climate change. In addition to flooding, risk monitoring and management systems have recently shown considerable shortfalls in planning for and responding to increased fire risk such as the devastating Californian wildfires in October 2019 ( [[#Morley--2020|Morley, 2020]] ) and Australia’s unprecedented and catastrophic 2019–2020 wildfire season. Risk management has also been challenged by new risk experiences including wild/bush fires encroaching on expanding urban areas and fire outbreaks in densely populated informal settlements pose increasing threats to livelihoods, human health and habitats globally (see also Sections 2.4.4.2 and 2.5.5.2).

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==== 6.3.3.4 Climate Resilient Health Systems ====

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Climate resilient health systems are a vital part of adaptation to protect the most vulnerable from climate change ( [[#WHO--2020|WHO, 2020]] ). Cardiovascular fitness for example is a root cause of morbidity and mortality form heat stress (Schuster et al., 2017). The World Health Organization has developed a framework of climate-resilient health systems that addresses both mitigation and adaptation goals ( [[#WHO--2015|WHO, 2015]] ). Universal health coverage (UHC) is an essential component of climate-resilient health systems. In most countries, access to health services is better in urban than in rural areas. However, there remain large urban populations with insufficient coverage of health services ( [[#WHO%20and%20WB--2015|WHO and WB, 2015]] ) and UHC tracking needs to take better account of inequalities in coverage, including differences in access within cities and further disaggregation of urban populations by income. Thus, health sector investment is an important tool in adaptive action and capacity. Analyses of health survey data shows that, globally, access to health care is increasing toward UHC targets (Lozano et al., 2020). Financing for global health has increased steadily in the last two decades and modelling shows this trend is ''likely'' to continue to 2050, but at a slower pace of growth and the current disparities in per-capita health spending persist between high and low/middle income countries, leading to insufficient health service coverage for the poorest populations (Chang et al., 2019a). Out-of-pocket spending is projected to remain substantial in LMIC and will remain the only means to access health care for many poor urban populations.

The WHO Operational Framework highlights the components that can be strengthened to adapt to extreme weather (e.g., health care workforce, information systems, etc.). The evidence is greatest for impacts on larger health facilities (such as hospitals) and there is less evidence regarding impacts on health service delivery outside these settings (smaller health facilities, pharmacies, first responders, public health inspectors, etc.). Improved building design and spatial urban planning (where facilities are located) are essential to increase resilience for higher temperature and flood risk ( ''medium evidence'' ; ''high agreement'' ) ( [[#WHO--2021|WHO, 2021]] ; [[#Codjoe--2020|Codjoe et al., 2020]] ; [[#Korah--2017|Korah and Cobbinah, 2017]] ). Public health systems rely on information systems (including disease and vector surveillance and monitoring) to identify new and emergent public health risks. Improvements to health surveillance will increase resilience, particularly for populations in informal settlements that are absent from health and vital registration systems.

City-level and local government adaptation planning is facilitated by information on health impacts (Reckien et al., 2015), highlighting the need for monitoring and surveillance and the need for local evidence-based risk assessments. Adaptation in the health sector can be limited by lack of collaboration between health and other sectors, although this is often easier to facilitate at the local level (Woodhall, Landeg and Kovats, 2021).

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==== 6.3.3.5 Education and Communication ====

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Since AR5, there has been significant growth in research about climate education and activism (Simpson, Napawan and Snyder, 2019; O’Brien, Selboe and Hayward, 2018; [[#Hayward--2021|Hayward, 2021]] ). Access to knowledge is an important determinant of well-being, inclusivity and livelihood mobility and of driving human behaviour. Knowledge systems include formal educational provision (capital assets, syllabus and human capital), informal learning based in social interaction and customary institutions (including through social media) and public communication (news media, government and other information systems including commercial messaging). There is a growing body of literature addressing the role of information and communication technology in shaping behaviour in disaster response and recovery and climate action, with particular focus on social media use and serious gaming (Houston et al., 2015; Carson et al., 2018) (see [[#6.3.4.3|Section 6.3.4.3]] )

Given the amount of time that children spend in school settings, adapting educational infrastructure and programmes to climate change is highly important. This includes not only making physical structures safe, but also providing students with the knowledge and confidence to support individual and family-based adaptation. Several UN agencies (e.g., UNICEF and UNDRR) and international non-governmental agencies (e.g., Plan International) have prioritised safer schools and child-centred risk management that often focus on schools as places that should be prioritised for retrofitting and safe construction, but also as focal points for knowledge dissemination and community organising where impacts can extend beyond the school to reduce risk among students’ families. Universities and think tanks, as well as the third and private sector are key support mechanisms, particularly at the local level and when working in collaboration with local government and communities. They can support the development of critical educational resources and innovative communication methods, as well as facilitate the design and implementation of climate policies and related action plans.

Youth, adult communities, social media and the commercial media can have a significant impact on advancing climate awareness and the legitimacy of adaptive action, particularly in large urban areas ( ''medium evidence'' , ''high agreement'' ). Climate change education in urban settlements has increasingly focused on enhancing children and young people’s political agency in schools, universities, and in formal and informal media settings ( [[#Cutter-Mackenzie--2019|Cutter-Mackenzie and Rousell, 2019]] ). However, an ambiguous framing of climate impacts and adaptation, for example around the science of urban heat islands by the media, can also exacerbate local community confusion and uncertainty (Iping et al., 2019) and further training and capacity building opportunities such as for vocational qualifications is still required across diverse settings ( [[#Simmons--2021|Simmons, 2021]] ). Communication strategies deployed in formal education and social media can be highly influential in exchanging information and establishing narratives and viewpoints that frame what adaptive action is legitimate, especially in large cities (Simpson, Napawan and Snyder, 2019). However, the effectiveness of communication strategies for change, for example from Mayoral offices, can also be influenced by wider political and structural drivers including community literacy or political partisanship (Boussalis, Coan and Holman, 2019). Recent research (e.g., Macintyre et al., 2018) highlights the need for new learning approaches to climate education from school age to adult education. Emphasis is on inclusivity in learning and recognising diverse perspectives across multiple levels and settings, from formal and informal education to wider social learning. Informal learning that takes place outside of school settings, such as in libraries and botanical gardens, in everyday life is increasingly recognised as a key arena for climate education, life-long learning and nurturing environmental citizenship and activism (Paraskeva-Hadjichambi et al., 2020).

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==== 6.3.3.6 Cultural heritage/institutions ====

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The integration of culture into urban policy and planning is increasingly recognised as critical to developing sustainable and resilient cities, and features in international agreements such as the SDGs ( ''limited evidence'' ; ''high agreement'' ) ( [[#Sitas--2020|Sitas, 2020]] ). However, urban cultural policies are still limited, for example, Cape Town is the only African city to have developed a city-level cultural policy ( [[#Sitas--2020|Sitas, 2020]] ). Cultural heritage refers to both tangible (e.g., historic buildings and sites) and intangible (e.g., oral traditions and social practices) resources inherited from the past ( [[#Fatorić--2020|Fatorić and Egberts, 2020]] ; Jackson, Dugmore and Riede, 2018). Learning about past societal and environment changes through heritage offers opportunity for reflection and transfer of knowledge and skills. This takes place in multiple contexts such as museums and cultural landscapes, and in everyday life ( [[#Fatorić--2020|Fatorić and Egberts, 2020]] ; Jackson, Dugmore and Riede, 2018). Cultural heritage is primarily associated with identity and is closely intertwined with the complexities of history, politics, economics and memory. Climate change adds another layer of complexity to cultural heritage and resource management ( [[#Fatorić--2017b|Fatorić and Seekamp, 2017b]] ). Changing climatic conditions are already negatively impacting World Heritage Sites such as the Cordilleras’ Rice Terraces of the Philippines and earthen architecture sites, for example the Djenné mosque in Mali, are particularly vulnerable to changes in temperature and water interactions ( [[#UNESCO--2021|UNESCO, 2021]] ). Climate change impacts intangible cultural heritage across diverse settings such as in the Caribbean and Pacific Small Island Developing States (SIDS) where traditional ways of life and related aspects such as oral traditions and performing arts are under threat from extreme weather events ( [[#UNESCO--2021|UNESCO, 2021]] ).

The climate change adaptation options for built cultural heritage fall into seven categories (Rockman et al., 2016; [[#Fatorić--2017b|Fatorić and Seekamp, 2017b]] ). Financial constraints are the primary barriers that underpin the first four adaptation options: no action at all, merely monitoring and/or documenting, or annual maintenance (Xiao et al., 2019; Sesana et al., 2019; [[#Fatorić--2017a|Fatorić and Seekamp, 2017a]] ; [[#Fatorić--2017b|Fatorić and Seekamp, 2017b]] ; [[#Fatorić--2018|Fatorić and Seekamp, 2018]] ). Core and shell preservation, the fifth and sixth categories, are cost effective when they improve the condition of built cultural heritage (BCH) ( [[#Bertolin--2018|Bertolin and Loli, 2018]] ; [[#Loli--2018a|Loli and Bertolin, 2018a]] ; [[#Loli--2018b|Loli and Bertolin, 2018b]] ), while elevation and/or relocation, the final adaptation options, are extremely costly and might jeopardise the historic value (Xiao et al., 2019). To date, however, evidence indicates that adaptation actions prioritise archaeological sites (Carmichael et al., 2017; [[#Fatorić--2018|Fatorić and Seekamp, 2018]] ; Pollard et al., 2014; [[#Dawson--2013|Dawson, 2013]] ). The efficacy of adaptation of historic buildings can be increased through increased and stable funding, incentives, stakeholder engagement, and legal and political frameworks (Dutra et al., 2017; [[#Fatorić--2018|Fatorić and Seekamp, 2018]] ; [[#Fatorić--2017b|Fatorić and Seekamp, 2017b]] ; [[#Fatorić--2017a|Fatorić and Seekamp, 2017a]] ; [[#Leijonhufvud--2016|Leijonhufvud, 2016]] ; [[#Phillips--2015|Phillips, 2015]] ; Sesana et al., 2019; Sesana et al., 2018; [[#Sitas--2020|Sitas, 2020]] ).

Other barriers to implementation include harnessing expert and local knowledge (of individuals and organisations) to identify both quantitative and qualitative methods and indicators that connect cultural significance and local values vis-à-vis climatic change over time and that move beyond the prevalent high-risk or high-vulnerability centred approaches (Carmichael et al., 2017; [[#Fatorić--2018|Fatorić and Seekamp, 2018]] ; Haugen et al., 2018; [[#Leijonhufvud--2016|Leijonhufvud, 2016]] ; Pollard et al., 2014; Puente-Rodríguez et al., 2016; Richards et al., 2018; [[#Dawson--2013|Dawson, 2013]] ; Filipe, Renedo and Marston, 2017; Kotova et al., 2019). This is particularly important given that the significance of cultural heritage is often intangible, and its value cannot be determined solely through quantitative indicators. Accessing local resources (craftsmanship and materials compatible with the originals) can also improve built cultural heritage’s adaptation capacity ( [[#Phillips--2015|Phillips, 2015]] ).

Effective decision-making and practice for adapting built and intangible cultural heritage requires open dialogue and exchange of cultural, historical and technical information between diverse stakeholders and decision makers ( [[#Fatorić--2017b|Fatorić and Seekamp, 2017b]] ; Benson, Lorenzoni and Cook, 2016). As noted in [[#6.2.6|Section 6.2.6]] , human behaviour can be a driving force for adaptation impacts on BCH at risk. Despite challenges associated with intangibility, socio-cultural heritage such as Indigenous knowledge (e.g., food security and water management practices) presents important opportunities for climate adaptation and resilience building. More research is needed across diverse contexts to understand feasible climate adaptation measures, and barriers and opportunities for building the resilience of both built and intangible cultural heritage, as well as to increase awareness of cultural heritage benefits among climate change policymakers ( [[#Fatorić--2020|Fatorić and Egberts, 2020]] ).

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<span id="adaptation-through-nature-based-solutions"></span>
=== 6.3.4 Adaptation Through Nature-Based Solutions ===

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Well-functioning ecosystems can play a significant role in buffering cities, settlements and infrastructure from climate hazards at multiple scales ( ''robust evidence'' , ''high agreement'' ). Nature-based solutions (NBS) are actions to protect, sustainably manage and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits (Cohen-Shacham et al., 2016). Widely recognised as low-regret measures for disaster risk reduction and climate change adaptation, green and blue infrastructure investments and natural area conservation in cities can provide NBS across scales to reduce temperature shocks and provide natural flood defences among other adaptation and resilience benefits (McPhearson et al., 2018; Andersson et al., 2019; Frantzeskaki et al., 2019). Blue infrastructure, for example, provides ecological and hydrological functions (e.g., evaporation, transpiration, drainage, infiltration, detention) critical to sustainable urban water management (Iojă et al., 2021). Public parks, urban forests, street trees and green roofs, as well as lakes, ponds and streams are widely documented for providing local cooling, grass and riparian buffers, forested watersheds can enhance flood and drought protection for cities and settlements, and mangrove stands and wetlands in coastal areas can reduce storm surges. Despite increasing knowledge about NBS (here encompassing literature on ecosystem services for climate change adaptation and resilience, ecosystem-based adaptation, and benefits of green and blue infrastructure for adaptation), recent studies indicate that nature-based approaches to adaptation and resilience are still under-recognised and under-invested in urban planning and development (Matthews, Lo and Byrne, 2015; [[#Geneletti--2016|Geneletti and Zardo, 2016]] ; Frantzeskaki et al., 2019), despite the potential scale of benefits, for example, a recent study covering 70 cities in Latin America calculated that 96 million people would benefit from improving main watersheds with green infrastructure (Tellman et al., 2018).

Grey infrastructure often damages or eliminates biophysical processes (e.g., through soil sealing, stream burial or altered hydrology) necessary to sustain ecosystems, habitats and livelihoods, where urban ecological infrastructure (Childers et al., 2019) can be more flexible and cost effective for providing flood risk reduction and other benefits (Palmer et al., 2015). Hybrid approaches are emerging that integrate ecological and grey (engineered) infrastructure in adaptation planning and hazard protection (Grimm et al., 2016; [[#Depietri--2017|Depietri and McPhearson, 2017]] ). Explicit policy uptake by city authorities is increasing (Hansen et al., 2015; Hölscher et al., 2019), such as in New York where in 2010 the city committed to a hybrid infrastructure plan for storm water management, investing USD 5.3 billion over 20 years, of which USD 2.4 billion was targeted for green infrastructure investments ( [[#NYC--2010|NYC, 2010]] ). A subset of services from urban ecosystems are being increasingly invested in as NBS for climate adaptation pathways (Keeler et al., 2019; Kabisch et al., 2016) and included as regulatory drivers through flood management, hazard mitigation and air pollution regulations that encourage or enforce the implementation of green infrastructure practices (Davis et al., 2020).

Development and climate mitigation co-benefits of NBS is an additional reason that NBS are being increasingly taken up by cities, including for improving health and livelihoods, particularly for poor, marginalised groups (Poulsen et al., 2015; Poulsen, Neff and Winch, 2017; Maughan, Laycock Pedersen and Pitt, 2018; [[#Simon-Rojo--2019|Simon-Rojo, 2019]] ; [[#Cederlöf--2016|Cederlöf, 2016]] ). Co-benefits include a wide range of social and environmental benefits (Brink et al., 2016; Alves et al., 2019) for human physical and mental health (Kabisch, van den Bosch and Lafortezza, 2017; Sarkar, Webster and Gallacher, 2018; Engemann et al., 2019; Rojas-Rueda et al., 2019), climate mitigation (De la Sota et al., 2019) and as habitat for local biodiversity ( [[#Ziter--2016|Ziter, 2016]] ; Knapp, Schmauck and Zehnsdorf, 2019). At the same time, concerns about the unintended consequences of investing in green infrastructure for NBS, such as how it may contribute to gentrification (Turkelboom et al., 2018; Anguelovski et al., 2018; Haase et al., 2017), create more public use, increase water demand (Nouri, Borujeni and Hoekstra, 2019) or contribute to criminal activity ( [[#Cilliers--2015|Cilliers and Cilliers, 2015]] ) underlines the challenges of investing in adaptation in complex urban systems (see [[#6.2.6|Section 6.2.6]] ). Additionally, more place-based analyses of the efficacy of NBS for reducing climate impacts across varying urban contexts and future climate scenarios are needed to better understand the cost effectiveness of investing in NBS to provide disaster risk reduction and deliver critical co-benefits for human well-being. Cooperation between scientists, decision-makers and Indigenous knowledge-holders can supplement current efforts and ensure that investments in NBS do not negatively impact indigenous communities (Ban et al., 2018; Seddon et al., 2021; Townsend, Moola and Craig, 2020).

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<span id="temperature-regulation"></span>
==== 6.3.4.1 Temperature Regulation ====

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Nature-based strategies, including street trees, green roofs, green walls and other urban vegetation, can reduce heat and extreme heat by cooling private and public spaces ( ''robust evidence'' , ''high agreement'' ). Shading and evapotranspiration are the primary mechanisms for vegetation-induced urban cooling (Coutts et al., 2016). Shading reduces mean radiant temperature, which is the dominant influence on outdoor human thermal comfort under warm, sunny conditions (Thorsson et al., 2014; Viguié et al., 2020). Outdoor green space and parks may also slightly reduce indoor heat hazard (Viguié et al., 2020). Apart from lowering temperature, NBS may also contribute to lower energy costs by reducing extra demand for conventional sources of cooling (e.g., air conditioning) (Viguié et al., 2020; Foustalieraki et al., 2017), especially during peak demand periods. Homes with shade trees that are located in cities where air conditioning systems are common can save over 30% of residential peak cooling demand (Zardo et al., 2017; Wang et al., 2015). Green roofs have been shown to significantly lower surface temperatures on buildings (Bevilacqua et al., 2017) and modelling suggests that green roofs, if employed widely throughout urban areas, have the potential to impact the regional heat profile of cities (Bevilacqua et al., 2017; Rosenzweig, Gaffin and Parshall, 2006). Community or allotment gardens, backyard greening and other types of low vegetation, as well as lakes, ponds, rivers and streams, can also provide local cooling benefits to nearby residents (Gunawardena, Wells and Kershaw, 2017; Larondelle et al., 2014; [[#Santamouris--2020|Santamouris, 2020]] ).

Urban climate models show that increased vegetation cover results in reducing both mean air temperatures and extreme temperatures during heatwaves (Heaviside, Cai and Vardoulakis, 2015; [[#Ferreira--2019|Ferreira and Duarte, 2019]] ; [[#Schubert--2013|Schubert and Grossman-Clarke, 2013]] ). Greater density and more canopy coverage relative to other built and paved surfaces increases shade provision and evapotranspiration (Hamstead et al., 2016; Grilo et al., 2020; Herath, Halwatura and Jayasinghe, 2018; Knight et al., 2021). However, local cooling by vegetation depends on regional climate context, geographic setting of the city, urban form, the density and placement of the trees, in addition to a variety of other ecological, technical, and social factors, such as local stewardship (Salmond et al., 2016). Green spaces less than 0.5–2.0 ha may have negligible cooling effects at regional scales, but impacts of shading can have microscale cooling benefits (Gunawardena, Wells and Kershaw, 2017; Zardo et al., 2017). Vegetation impacts on day versus night-time cooling varies (Imran et al., 2019) as does cooling potential in temperate versus tropical climates. The supply of cooler air from surrounding peri-urban and rural areas can impact cooling in the urban core suggesting that regional adaptation planning for NBS is important to maintain or extend ventilation paths from the urban fringe into the city centre (Schau-Noppel, Kossmann and Buchholz, 2020).

To maximize the adaptation benefits of NBS for regulating urban heat, it can be helpful to prioritise tree planting and other urban greening investments in areas where heat vulnerability and risk are the highest, especially communities that lack urban tree canopy or accessibility to parks to cool off during hot days or heatwaves (Ziter et al., 2019). Planting trees closely together or in partly permeable vegetated barriers along streets can improve local cooling benefits. Additionally, choosing tree species with leaves that have the greatest leaf area index or the largest leaves can improve cooling performance, as those trees have the greatest shading and evapotranspiration benefits that, in turn, provide the greatest cooling effects (Keeler et al., 2019). Drought-resistant trees, often native trees, are ideal to avoid high watering costs, though dry or water scarce areas may limit adoption of urban vegetation as an NBS strategy (Coutts et al., 2013). Native trees and permaculture can provide additional benefits for local biodiversity as shown in study in Melbourne, Australia which found that increasing vegetation from 10% to 30% increased occupancy of bats, birds, bees, beetles and bugs by up to 130% (Threlfall et al., 2017), with particularly high impact on native species.. Additionally, planting fruit or nut trees can provide co-benefits for local food production, and yet choice of species and placement is important to consider with respect to local cultural needs and norms ( [[#Adegun--2018|Adegun, 2018]] ; [[#Adegun--2017|Adegun, 2017]] ).

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==== 6.3.4.2 Air Quality Regulation ====

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NBS in cities can help regulate air quality by absorbing air pollutants ( ''medium evidence'' , ''medium agreement'' ). For example, planting trees or vegetated barriers along streets or in urban forests can reduce particulate matter, the ambient air pollutant with the largest global health burden ( [[#Janhäll--2015|Janhäll, 2015]] ; Tiwary, Reff and Colls, 2008; Matos et al., 2019; McDonald et al., 2016). However, findings show that trees can also positively affect ground-level ozone (Calfapietra et al., 2013; Kroeger et al., 2014), airborne pollen concentrations ( [[#Willis--2017|Willis and Petrokofsky, 2017]] ) and indirectly affect air quality through reduced emissions from energy production offset by shade provision (Keeler et al., 2019). Certain tree species however can also be detrimental to urban ozone formation by emitting significant amounts of reactive biogenic volatile organic compounds (VOCs). Decreasing urban emissions of VOCs is an increasingly important ozone mitigation strategy in urban areas (Fitzky et al., 2019).

Trees can also have negative effects by increasing pedestrian exposure to pollution if they are introduced in heavily travelled street canyons where air pollutants can be trapped (Vos et al., 2013; [[#Gromke--2015|Gromke and Blocken, 2015]] ). To maximise the adaptation benefits of NBS for improving air quality, planners and managers can target tree selection for species with low VOC emissions, low allergen emissions and high pollutant deposition potential (Keeler et al., 2019), and combine with low pollution transportation policies. Studies suggest sensitive planting of roadside tree canopies can have positive effects on air pollutants (Beckett, Freer Smith and Taylor, 2000; Yang, Chang and Yan, 2015). For example, [[#Xue--2021|Xue et al. (2021)]] found that the PM2.5 reduction between 2013 and 2017 in China was associated with a saving of approximately USD 111 billion yr -1 nationally. Tree planting near schools, nursing homes and hospitals can ensure that benefits provided by trees are delivered to the local populations that stand to benefit the most from improved air quality, but species need to be adapted to regional climate to provide benefits over time ( [[#Donovan--2017|Donovan, 2017]] ; Nowak et al., 2018).

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==== 6.3.4.3 Stormwater Regulation and Sanitation ====

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Urban parks and open spaces, forests, wetlands, green roofs and engineered stormwater treatment devices help manage stormwater and wastewater by reducing the volume of stormwater runoff, reducing surface flooding, and reducing contamination of runoff by pollutants ( ''robust evidence'' , ''high agreement'' ). Engineered devices include bioswales, rain gardens, and detention and retention ponds, and are becoming common and standard approaches to mitigate the negative effects of impervious surfaces on stormwater quality and surface flooding in cities ( [[#Zhou--2014|Zhou, 2014]] ; McPhillips et al., 2020). Allotment gardens, street trees, green roofs and urban forests may also help reduce runoff and provide a stormwater retention service (Pennino, McDonald and Jaffe, 2016; Berland et al., 2017; Gittleman et al., 2017). Modelling and empirical studies show that NBS at small spatial scales lead to improvements in water quality and reduction of peak flows (Moore et al., 2016; Keeler et al., 2019; Webber et al., 2020). Peak flow reductions are greatest for small rain events. For example, D-Ville et al. (2018) observed a 30–70% reduction in peak flow for the 1-in-30 year storm, but performance reduces for more intense rainfall or if saturated (Garofalo et al., 2016). Employing NBS to reduce flooding on roads can be an important adaptation mechanism for reducing the impact of flooding events on traffic flows (Pregnolato et al., 2016).

During periods with intense precipitation, low-lying urban parks and open space, engineered devices and wetlands can play an important role in reducing stormwater runoff volumes by providing places for water to be stored and infiltrate during heavy storms (Moore et al., 2016). However, the magnitude of the runoff reduction service will depend on the total area of green infrastructure, vegetation type and its position on the landscape. There is less evidence of the effectiveness of NBS at larger temporal and spatial scales (Pregnolato et al., 2017; Jefferson et al., 2017). The performance of NBS depends on the degree to which their extent and spatial configuration in the city are optimised to capture runoff ( [[#Fry--2017|Fry and Maxwell, 2017]] ). Investing in a diversity of NBS types may be important to maximise stormwater management and flood regulation, as different types of engineered NBS have different strengths and weaknesses.

Overall, NBS are attractive adaptation options for stormwater management and to reduce impacts of pluvial and fluvial flooding in cities (Rosenzweig et al., 2018a) compared, and in combination, with grey infrastructure. Cities with combined sewer infrastructure are ''likely'' to see benefits from NBS due to reductions in stormwater quantity and reduced sewage overflows. Cities where a large proportion of residents lack access to piped infrastructure and drink surface water may see large benefits, especially to human health, from NBS investments (Keeler et al., 2019). Where future large-scale upgrades or installation of grey infrastructure will be necessary, new and growing cities may have more opportunity to realise large net benefits from investments in NBS. Older cities, and new, rapidly urbanising areas that lack large-scale water infrastructure may see the greatest benefits from enhanced NBS, relative to cities where heavy investments infrastructure upgrades have already been made. Cities facing climate changes that include more frequent or extreme precipitation may also see large water quality benefits from investment in NBS (Keeler et al., 2019). Overall, there is increasing evidence that NBS for addressing stormwater is cost effective (Bixler et al., 2020; Kozak et al., 2020; Mguni, Herslund and Jensen, 2016), especially in cities facing a need to update current infrastructures.

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==== 6.3.4.4 Coastal Flood Protection ====

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Coastal ecosystems including coral and oyster reefs, coastal forests including mangroves and other tree species, salt marshes and other types of wetland habitat, seagrass, dunes and barrier islands can reduce impacts of coastal flooding and storms ( ''robust evidence'' , ''high agreement'' ) (Zhao, Roberts and Ludy, 2014; [[#Boutwell--2016|Boutwell and Westra, 2016]] ; Narayan et al., 2017; Yang, Kerger and Nepf, 2015; Bridges et al., 2015; [[#World%20Bank--2016|World Bank, 2016]] ) (see also Section CCP2 Cities and Settlements by the Sea). Recent literature highlights the value of nature-based approaches for coastal protection in terms of avoided damages and human well-being (Narayan et al., 2017; Silva et al., 2016a). NBS can protect coasts from flooding through reducing the wave energy by drag friction, reducing wave overtopping by eliminating vertical barriers, and absorbing floodwaters in soil (Arkema, Scyphers and Shepard, 2017; Dasgupta et al., 2019; Zhu et al., 2020). For example, coastal and marine vegetation and reefs can dissipate wave energy, attenuate wave heights and nearshore currents, decrease the extent of wave run-up on beaches, and trap sediments (Ferrario et al., 2014; Bridges et al., 2015). These effects result in lower water levels and reduce shoreline erosion, which in turn has potential to save lives and prevent expensive property damages (Narayan et al., 2017).

Researchers, practitioners and policy-makers are increasingly calling for the use of nature-based approaches to protect urban shorelines from coastal hazards ( [[#Cunniff--2015|Cunniff and Schwartz, 2015]] ; Bilkovic et al., 2017). The expectation is that coastal ecosystems can help stabilise shorelines, protect communities against storm surge and from tidal-influenced flooding, while providing other co-benefits for people and ecosystems. However, vegetation along protected coastlines with higher frequency, lower intensity coastal hazards ( [[#National%20Research%20Council--2014|National Research Council, 2014]] ) may be more effective for stabilising shorelines and reducing risk to coastal communities and properties, and benefits will depend on local hydrology of the coastal region. [[#Narayan--2017|Narayan et al. (2017)]] estimate that coastal wetlands alone reduced direct flood damages by USD 625 million during Hurricane Sandy in the USA in 2012. Similarly, researchers found that villages with wider mangroves between them and the coast experienced significantly fewer deaths than villages with narrow or no mangroves during a 1999 cyclone in India ( [[#World%20Bank--2016|World Bank, 2016]] ). Recently, Arkema et al. (2017) noted that the number of people, poor families, elderly and total value of residential property most exposed to hazards along the entire coast of the USA can be reduced by half if existing coastal habitats remain fully intact.

Coastal habitats also have limitations in their ability to protect coasts from extreme events. Some studies suggest reduced effectiveness of vegetation and reefs for coastal protection from large storm waves and surge (Möller et al., 2014; Guannel et al., 2016) and there is active debate in the literature about the ability of ecosystems to mitigate the impact of tsunamis (Gillis et al., 2017). Further research is needed to understand and quantify coastal protection services provided by these hybrid green-grey solutions, especially in urban areas (Bilkovic et al., 2017). Additionally, in some coastlines, water may be too deep or waves too high for some species such as mangroves to grow, thrive and provided needed NBS.

Maximising the adaptation benefits of NBS for improving coastal flood protection research requires that cities seek to restore and conserve the vegetation and reef types that are appropriate for the exposure setting and in sufficient abundance to be effective. In particular, planners and managers can use vegetation in protected bays as alternatives to hard infrastructure for shoreline stabilisation. However, the influence of ecosystems on flooding and erosion is variable and depends on a suite of social, ecological and infrastructural factors that vary within and among urban areas (Narayan et al., 2017; Ruckelshaus et al., 2016; Bridges et al., 2015). Additionally, long-term planning to restore or ensure resilience of individual species and ecosystems that may themselves be damaged or destroyed during extreme events is needed in order for urban green and blue infrastructure to continue providing NBS over the longer term.

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==== 6.3.4.5 Riverine Flood Impact Reduction ====

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NBS reduce both the volume of floodwater and the impact of floods ( ''medium evidence'' , ''medium agreement'' ). NBS reduce the volume of runoff by increasing infiltration and water storage (Shuster et al., 2005; Salvadore, Bronders and Batelaan, 2015), and affect the production and impact of flood waters through reducing river energy and flow speed through physical blockage, stabilising riverbanks during flood events, creating space for floodwaters to expand and combating land subsidence (Palmer, Filoso and Fanelli, 2014; Ahilan et al., 2018). Installing NBS to increase infiltration on low slopes and high-permeability soils can reduce the impacts of potential increases in urban flooding driven by climate change, especially for small- to medium-scale flood events (lower than 20% mean annual flood) (Moftakhari et al., 2018).

Source reduction strategies include creating permeable areas such as parks and open spaces, as well as engineered devices such as raingardens, bioswales and retention ponds that help retain stormwater runoff from impervious areas. River restoration can reduce flood peak flow and provide space for floodwaters to expand. Planting and maintaining vegetation along riverbanks, often in the form of parks or river restoration, maintains structural integrity during flood events. Wetland construction and improved connectivity to floodplains also reduces flood peaks. Efforts to restore floodplains are important to create space for floodwaters and reduce exposure by moving people out of the hazard zone. Floodplain restoration also provides access to the river that has multiple benefits including recreation, access to water for domestic use and other cultural ecosystem services. A key adaptation strategy is to reduce streambank erosion (a result of high peak flow) using riparian vegetation to stabilise riverbanks during flood events.

Cities manage flood risk using different types of adaptation and regulatory mechanisms ( [[#Naturally%20Resilient%20Communities--2017|Naturally Resilient Communities, 2017]] ). Built flood-control infrastructure, such as levees and stream channelisation, reduces the demand for nature-based flood impact reduction. Cities facing flood risk that do not currently have extensive grey flood-mitigation infrastructure may find NBS to be an appealing, lower cost solution (Keeler et al., 2019). In cities where flood-control grey infrastructure already exists, there is less demand for NBS of flood protection, but NBS may provide important back up, especially in a changing climate that may increase flood hazards ( [[#City%20of%20Los%20Angeles--2017|City of Los Angeles, 2017]] ; Elmqvist et al., 2019). Overall, city and basin-wide NBS for riverine flood impact reduction can reduce the generation of new hazards by making space for water which can reduce the potential for a false sense of security provided by traditional flood management approaches (Ruangpan et al., 2020; Turkelboom et al., 2021).

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<span id="water-provisioning-and-management"></span>
==== 6.3.4.6 Water Provisioning and Management ====

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The role of NBS has been increasingly recognised for improving urban water management, emphasising it’s contribution for climate-adapted development and sustainable urbanisation ( ''robust evidence'' , ''high agreement'' ) ( [[#Wong--2009|Wong and Brown, 2009]] ). NBS that protect or restore the natural infiltration capacity of a watershed can increase the water supply service to various extents, improving drought protection and providing resilient water supply (Drosou et al., 2019; [[#Krauze--2019|Krauze and Wagner, 2019]] ), although different forms of NBS (e.g., street trees, parks and open space, community gardens, and engineered devices such as rain gardens, bioswales or retention ponds) contribute in different ways to increasing stormwater infiltration. Additional sources of water may be available to replace the water supplied by NBS, such as rainwater harvesting, inter-basin transfers or desalination plants. Reliance on naturally sourced, locally available surface water and groundwater is more energy efficient and economical than desalination or water reuse for potable use (Boelee et al., 2017), while rainwater harvesting is even more economical. Increasing the amount of green space in urban areas can secure and regulate water supplies, improving water security ( [[#Liu--2018|Liu and Jensen, 2018]] ; Bichai and Cabrera Flamini, 2018). However, [[#Bhaskar--2016|Bhaskar et al. (2016)]] reviewed the effect of urbanisation and NBS on baseflow and suggest that the confounded effects of infiltration and evapotranspiration losses, combined with the subsurface infrastructure (sewer systems) and geology, makes it difficult to predict the magnitude of baseflow enhancement resulting from the implementation of NBS in cities.

To maximise the adaptation benefits of NBS for urban water supply research suggests that managers and planners consider NBS as alternatives to traditional stormwater management techniques, where possible, since these solutions can promote groundwater recharge. As green infrastructure is increasingly being used for stormwater absorption in cities (McPhillips et al., 2020), rain gardens, wetlands, or engineered infiltration ponds and bioswales are the NBS most likely to promote recharge, reduce evapotranspiration and contribute to water provisioning.

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<span id="food-production-and-security"></span>
==== 6.3.4.7 Food Production and Security ====

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Urban agriculture can serve as a NBS for food security ( ''medium evidence'' , ''medium agreement'' ) across a range of urban contexts ( [[#Lwasa--2015|Lwasa and Dubbeling, 2015]] ; Nogeire-McRae et al., 2018; Pourias, Aubry and Duchemin, 2016) by contributing to food provisioning as well as providing co-benefits including for recreation, place making and mental health (Petrovic et al., 2019; Soga, Gaston and Yamaura, 2017; Goldstein et al., 2016b).

Urban agriculture among poorer communities in lower income areas is already an important source of food supply for those communities, contributing to food security and health (Orsini et al., 2013). However, potential for expanding open air urban food production may be practically constrained by land availability ( [[#Badami--2015|Badami and Ramankutty, 2015]] ; Martellozzo et al., 2014). This is particularly true in some lower-income countries where rapid urbanisation is occurring, which compounds existing food insecurity (Satterthwaite, McGranahan and Tacoli, 2010; Vermeiren et al., 2013). Land availability and suitability for gardens can be further constrained by land use history, including past industrial uses that can contaminate soils with pollutants such as lead.

At the same time, investments in vertical agriculture continue to expand, such as in Singapore where private investment in food production is occurring in high rise buildings (Wong, Wood and Paturi, 2020). Not all cities can benefit similarly from vertical agriculture since higher heating costs to produce vegetables indoors during northern winters consumes considerable amounts of energy and may generate fossil fuel emissions depending on the energy source (Goldstein et al., 2016a; Mohareb et al., 2017). Some regions can benefit from more traditional outdoor urban farming, such as in South and Southeast Asia, which can support multiple growing cycles per year for some crops, particularly in tropical areas where irrigation is available. Light availability, soil health and water availability will impact food production in urban areas. For example, a study conducted in Vancouver, Canada, demonstrated that light attenuation from buildings and trees can reduce both crop yield and water demand for crop growth (Johnson et al., 2015).

Climate change may have important impacts on urban food production and food security. While urban agriculture may provide benefits in terms of stability of food access in low-income households in some regions of the Global South where the climate is warmer, the shorter growing seasons in colder climates will reduce the role of outdoor urban agriculture in year-round food supply and diets. Though urban agriculture constitutes a small fraction of total food consumption in some urban areas, several studies have attempted to estimate the extent to which urban agriculture could theoretically meet urban total food or vegetable demand ( [[#Badami--2015|Badami and Ramankutty, 2015]] ; [[#McClintock--2014|McClintock, 2014]] ; Hara et al., 2018). Maximising the adaptation and resilience benefits of NBS for food production and security suggests the need to embrace the multi-functionality of urban agriculture, rather than viewing it as solely concerning food production (Barthel, Parker and Ernstson, 2015).

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=== 6.3.5 Adaptation Through Grey/Physical Infrastructure ===

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Globally, it is estimated that as much as USD 94 trillion of investment is required between 2016 and 2040 to replace, upgrade and extend the world’s physical infrastructure ( [[#Oxford%20Economics--2017|Oxford Economics, 2017]] ), much of which is ageing and will require replacement. Given the typical lifespan of infrastructure, this is both an opportunity and an imperative to ensure this investment is low carbon and resilient to climate change risks (Grafakos et al., 2020). ‘Grey’ or physical infrastructure is a priority for adaptation because its performance is sensitive to climate (particularly extreme events) and decisions on design and renovation have long-lasting implications and are hard to reverse (Ürge-Vorsatz et al., 2018). Avoiding longer-term impacts on society, the economy and the environment will require future investment and retrofitting of existing infrastructure, to be undertaken in the context of the risks of climate change (Dawson et al., 2018; Rosenzweig et al., 2018b). However, evidence from Africa shows that the benefits of pro-active adaptation measures and policies for infrastructure can result in net savings depending on the country context ( [[IPCC:Wg2:Chapter:Chapter-9#9.8.5|Section 9.8.5]] ).

Engineered measures for hazard mitigation such as seawalls, slope revetments and river levees, as well as air conditioning are increasingly implemented in urban centres, but many engineering interventions are less affordable and accessible in LMICs because of high construction and maintenance costs. These adaptive measures can also counter mitigation objectives because of reliance on climate-polluting energy sources. Despite this, engineering measures such as seawalls for tsunami protection and cooling areas in cities provide critical hazard reduction functions in urban contexts ( [[#Depietri--2017|Depietri and McPhearson, 2017]] ). As [[#Pelling--2018|Pelling et al. (2018)]] highlight, sustainable risk reduction can be better achieved where these engineering measures include the at-risk poor majority and inclusive planning to support pro-poor risk reduction. Inclusive design and management of physical infrastructure can enhance contributions to climate resilient development (Table 6.6 and Supplementary Material). This section covers urban morphology and built form, building design, information and communication technology, energy, transport, water and sanitation, and coastal management. All these domains of physical infrastructure will require adaptation to cope with a changing climate; many of them can also contribute to broader adaptation for cities and settlements.

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<span id="urban-morphology-and-built-form"></span>
==== 6.3.5.1 Urban Morphology and Built Form ====

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Urban morphology describes the overall status of cities as physical, environmental and cultural entities. Cities interact with surrounding environmental processes, for example, as documented in [[#6.2|Section 6.2]] by influencing urban temperature, but also precipitation and through coastal and riverine development fluvial and coastal sedimentary regimes of erosion and deposition that impact on flood risk. Rapid, increased urbanisation has contributed to observed flood risks in recent decades (see Section 5 4.2.4; Tramblay et al., 2019). The design process for physical infrastructure projects and significant construction (e.g., residential or industrial estates and large industrial development) typically includes risk assessments and social and environmental impact assessments that consider neighbouring land uses and connected infrastructure. Land use planning can consider diverse land uses and their interactions at the neighbourhood level ( [[#6.3.2|Section 6.3.2.1]] ). Resilience planning aims to bring together integrated, systemic views and enable joined-up planning at the city level (as well as lower scales) ( [[#6.3.2|Section 6.3.2.1]] ). There is however a lack of long-term studies that assess the climate change impacts on urban form, including informal settlements (Bai et al., 2018; Ramyar, Zarghami and Bryant, 2019), leading to impact assessments that often overlook urban form (Ramyar, Zarghami and Bryant, 2019). Additionally, context-specific spatial tools and community based approaches lack a precise connection to urban morphology. For example, there is a need for further studies that connect solar radiation, urban morphology (e.g., aspect and plot ratio), and the urban heat island spatio-temporal variability ( [[#Giridharan--2018|Giridharan and Emmanuel, 2018]] ; Li et al., 2019c).

Several tools and models have emerged in response to recommendations from AR5, including models that assess the impacts of urban heat island (Ramyar, Zarghami and Bryant, 2019), climatic uncertainty ( [[#Dhar--2017|Dhar and Khirfan, 2017]] ), flood vulnerability (Abebe, Kabir and Tesfamariam, 2018) and inundation (Barau et al., 2015; Ford et al., 2019). For example, findings from Kano, Nigeria, reveal that a lack of distribution of certain urban morphological features, including open spaces and streets (both pervious and impervious), roof and building materials (e.g., concrete and metallic) and urban ecological features (e.g., urban ponds and ecological basin), exacerbates inundations and their associated impacts (Barau et al., 2015). Also, findings about the urban forms of coastal settlements, particularly in small islands, reveal that they often experience severe beach erosion due to wave action, sea level rise and storm surge that leads to landward retreat of coastline which threatens their social and economic activities ( [[#Dhar--2016|Dhar and Khirfan, 2016]] ; Lane et al., 2015; [[#Khirfan--2019|Khirfan and El-Shayeb, 2019]] ). Despite these examples, very limited research is available to offer assessments of different urban scale morphologies and urban scale adaptation planning, including planning adaptation across supply chains and networked relationships with distant urban and rural places connected through trade and resource (financial, human and material) or waste flows.

Interventions in the morphology and built form of cities can contribute to the reduction of the urban heat island effect and reduce the consequences of urban heatwaves. These can include installing air conditioning, establishing public cooling centres (i.e., for use during heatwaves), pavement watering (Parison et al., 2020a) and increasing surface albedo through ‘cool roofs’ (i.e., with high-reflectance materials) and walls. Air conditioning can significantly increase the local urban heat island (Salamanca et al., 2014; Wang et al., 2019a) and the choice of refrigerant has a significant impact on global warming potential (McLinden et al., 2017). The relative efficiency of cool roofs compared with green roofs is variable, because while white roofs have similar potential to reduce the urban heat island (Li, Bou-Zeid and Oppenheimer, 2014), they can quickly turn grey due to dust and air pollution, losing their effectiveness (Gunawardena, Wells and Kershaw, 2017), although these effects are now well studied and newer performance standards should account for ageing and soiling effects on reflectivity (Paolini et al., 2014). Ageing of ‘cool pavements’ is more complex, which makes their long-term performance less reliable to predict (Lontorfos, Efthymiou and Santamouris, 2018). The cooling performance of green roofs is highly variable and depends on the actual water content of the green roof substrate, with dry vegetation performing poorly in terms of cooling (Parison et al., 2020b). This holds true for regular vegetation and NBS in general (Daniel, Lemonsu and Viguie, 2018). For all built environment adaptations, changes are locked-in for a long time, and are likely to be expensive so that care is needed to avoid potential negative impacts on social equity ( [[#Cabrera--2015|Cabrera and Najarian, 2015]] ; Romero-Lankao et al., 2018; Fried et al., 2020; Rode et al., 2017) and carbon-intensive construction (Bai et al., 2018; Seto et al., 2016).

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<span id="building-design-and-construction"></span>
==== 6.3.5.2 Building Design and Construction ====

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Architectural and urban design regulations at the single-building scale (building codes and guidelines) facilitate climate responsive buildings that adapt to a changing climate and have the potential to collectively change user behaviour during extreme weather events ( [[#Osman--2019|Osman and Sevinc, 2019]] ). They include buildings that are adaptive to ensure user comfort during extremes of hot and cold as well as to floods (e.g., building on stilts and amphibian architecture). Changes to design standards can scale quickly and widely, but retrofit of existing buildings is expensive, so care must be taken to avoid potential negative impacts on social equity (Schünemann et al., 2020; Matopoulos, Kovács and Hayes, 2014; [[#Ajibade--2014|Ajibade and McBean, 2014]] ; [[#Bastidas-Arteaga--2019|Bastidas-Arteaga and Stewart, 2019]] ). Buildings can be adapted to the negative consequences of climate change by altering their characteristics, for example increasing the insulation values (e.g., van Hooff et al., 2014; [[#Makantasi--2016|Makantasi and Mavrogianni, 2016]] ; [[#Fisk--2015|Fisk, 2015]] ; Fosas et al., 2018; Barbosa, Vicente and Santos, 2015; [[#Invidiata--2016|Invidiata and Ghisi, 2016]] ; Pérez-Andreu et al., 2018; Taylor et al., 2018; Triana, Lamberts and Sassi, 2018), adding solar shading (e.g., van Hooff et al., 2014; [[#Makantasi--2016|Makantasi and Mavrogianni, 2016]] ; Barbosa, Vicente and Santos, 2015; [[#Invidiata--2016|Invidiata and Ghisi, 2016]] ; Pérez-Andreu et al., 2018; Taylor et al., 2018; Triana, Lamberts and Sassi, 2018; [[#Dodoo--2016|Dodoo and Gustavsson, 2016]] ; [[#Osman--2019|Osman and Sevinc, 2019]] ), increasing natural ventilation, preferably during the night (e.g., van Hooff et al., 2014; [[#Makantasi--2016|Makantasi and Mavrogianni, 2016]] ; Pérez-Andreu et al., 2018; Triana, Lamberts and Sassi, 2018; [[#Dodoo--2016|Dodoo and Gustavsson, 2016]] ; [[#Osman--2019|Osman and Sevinc, 2019]] ; [[#Mulville--2016|Mulville and Stravoravdis, 2016]] ; Cellura et al., 2017; Fosas et al., 2018; Dino and Meral Akgül, 2019), solar orientation of bedroom windows (Schuster et al., 2017), applying high-albedo materials for the building envelope (van Hooff et al., 2014; [[#Invidiata--2016|Invidiata and Ghisi, 2016]] ; Baniassadi et al., 2018; Triana, Lamberts and Sassi, 2018), altering the thermal mass (van Hooff et al., 2014; [[#Mulville--2016|Mulville and Stravoravdis, 2016]] ; [[#Din--2017|Din and Brotas, 2017]] ), adding green roofs/facades to poorly insulated buildings ( [[#Geneletti--2016|Geneletti and Zardo, 2016]] ; Skelhorn, Lindley and Levermore, 2014; van Hooff et al., 2014; de Munck et al., 2018; [[#Feitosa--2018|Feitosa and Wilkinson, 2018]] ) and for water harvesting (Sepehri et al., 2018).

In general, the most promising adaptation measures are a combination of solar shading with increased levels of insulation and ample possibilities to apply natural ventilation to cool down a building (e.g., van Hooff et al., 2014; [[#Makantasi--2016|Makantasi and Mavrogianni, 2016]] ; Fosas et al., 2018; Barbosa, Vicente and Santos, 2015; Taylor et al., 2018; Triana, Lamberts and Sassi, 2018; [[#Dodoo--2016|Dodoo and Gustavsson, 2016]] ). However, it must be noted that the cooling potential of natural ventilation will decrease in the future because of increasing outdoor air temperatures ( [[#Gilani--2020|Gilani and O’Brien, 2020]] ). Increased insulation (including through green solutions) without shading and ventilation can also lead to adverse impacts through the lowering of nighttime cooling (Reder et al., 2018). Similarly, air conditioning performance also decreases with increasing outdoor temperatures, in addition to being maladaptive where use increases anthropogenic heat emissions into the urban area, and global greenhouse gas emissions if powered by carbon intensive energy systems (Wang et al., 2018c).

Passive cooling is a design-based, widely used strategy to create naturally ventilated buildings, making it an important alternative to address the urban heat island for residential and commercial buildings (Al-Obaidi, Ismail and Rahman, 2014). Generally, passive cooling is achieved by controlling the interactions between the building envelope and the natural elements. Façade fixes such as overhangs, louvres and insulated walls are effective at shading buildings from solar radiation, while complex ones such as texture walls, diode roofs and roof ponds are effective at minimising heat gains from solar radiation and ambient heat ( [[#Oropeza-Perez--2018|Oropeza-Perez and Østergaard, 2018]] ). Passive cooling is inspired also by traditional design forms, for example from Mediterranean, Islamic and Mughal architecture in the Indian sub-continent ( [[#Di%20Turi--2017|Di Turi and Ruggiero, 2017]] ; Izadpanahi, Farahani and Nikpey, 2021).

In addition, wind towers, solar chimneys and air vents are features that facilitate cool air circulation within buildings while dissipating heat (Bhamare, Rathod and Banerjee, 2019). These features may be arranged to address hotspots or highly frequented spaces within buildings. Similar to NBS, the effectiveness of passive cooling to ameliorate the urban heat island varies widely depending on the location of the sun, wind direction and the type of strategy used. For instance, natural ventilation strategies (e.g., wind towers, solar chimneys, etc.) have shown temperature reductions of up to 14°C (Bhamare, Rathod and Banerjee, 2019; [[#Calautit--2016|Calautit and Hughes, 2016]] ; Rabani et al., 2014). Shading strategies alone can reduce indoor temperatures by 3°C, while heat sinks (in which heat is directed at a medium such as water) may result in indoor temperatures up to 6°C lower than the outdoor temperature ( [[#Oropeza-Perez--2018|Oropeza-Perez and Østergaard, 2018]] ). More systemic interventions, such as altering urban form through urban planning, can mitigate the urban heat island across suburbs and cities ( [[#Lee--2019|Lee and Levermore, 2019]] ; [[#Takkanon--2019|Takkanon and Chantarangul, 2019]] ; Yin et al., 2018; [[#Liang--2015|Liang and Keener, 2015]] ; [[#Emmanuel--2018|Emmanuel and Steemers, 2018]] ). Experience in Kano (Nigeria) has shown that incorporating Indigenous knowledge into building design and urban planning can increase resilience to heat and flood risks (Barau et al., 2015). A review by [[#Lemi--2019|Lemi (2019)]] suggests that traditional ecological knowledge can provide wider climate change adaptation benefits.

Limits on housing and building adaptation include failure of regulatory systems so that formal design standards are not followed even when legally required (Arku et al., 2016; [[#Durst--2017|Durst and Wegmann, 2017]] ; [[#Pan--2012|Pan and Garmston, 2012]] ; [[#Awuah--2014|Awuah and Hammond, 2014]] ). This can be a result of pressures from clients for cheaper structures, developers illegally cutting costs or regulators lacking capacity for enforcement. Technological innovation can also be slow to embed itself in building norms and standards. Innovation also lies outside the formal sector and can include artisanal building techniques that may have adaptive value. Examples from Latin America demonstrate how initiatives in informal settlement improvement associated with housing policy, guaranteeing access to land and decent housing, show the opportunity for overarching policies encompassing development, poverty reduction, disaster-risk reduction, climate-change adaptation and climate-change mitigation (see [[IPCC:Wg2:Chapter:Chapter-12#12.5.5|Section 12.5.5]] ).

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==== 6.3.5.3 Information and Communication Technology ====

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Information and communication technologies (ICTs) are deeply intertwined with the functioning of urban and infrastructure systems, and are at the core of the ‘smart city’ concept ( [[#Angelidou--2015|Angelidou, 2015]] ). ICT is more flexible than other physical infrastructure, although as other sectors are increasingly reliant on ICT, it is creating new climate-related failure mechanisms ( [[#Norman--2018|Norman, 2018]] ; Maki et al., 2019). ICT assets and networks in urban, national and international communications systems will need to be strengthened to enable ICT infrastructure to better cope with climate change, and to enable ICT infrastructure to support the resilience of cities, settlements and other infrastructure. The increased pervasiveness of ICT in smart cities, smart infrastructure and day-to-day living, will evidently have long-term implications for exposure to climate change risks and how cities manage those risks ( [[#Norman--2018|Norman, 2018]] ; Maki et al., 2019). For example, even if the ICT network is resilient to heatwaves, it is dependent on the electricity network to power it. Conversely, other networks are dependent upon ICT for control systems, for example smart grids for energy. There is limited information on how these interdependencies, and associated risks, will evolve.

Although networked like many other infrastructure systems, ICT components have some distinctive properties. They are relatively cheap, and the advent of wireless communications has enabled ICT to have the widest reach of all infrastructures. Components can be rapidly deployed or repaired, and generally ICT networks are therefore built with inherent redundancy and flexibility (Sakano et al., 2016). Components have a wide range of expected lifetimes which leads to faster cycles of innovation. There is therefore greater potential to accelerate uptake of climate resilience in this infrastructure sector, but conversely, this can increase waste and (energy intensive) resource consumption. For example, mobile phones and computers may last as little as a year, cables and switching units may be moved and upgraded to improve bandwidth every few years, poles and masts are typically designed to last several decades, whilst exchanges and other critical nodes can be in use for over half a century.

ICTs are playing an increasing role in resilience building and enabling climate change adaptation. They are enabling access to information needed for decision making, facilitating learning and coordination among stakeholders, and building social capital, as well as helping to monitor, visualise and disseminate current and future climate impacts (Eakin et al., 2015; [[#Heeks--2019|Heeks and Ospina, 2019]] ; Haworth et al., 2018; Imam, Hossain and Saha, 2017). Advocacy and awareness raising through ICTs, such social media applications, can influence behaviours and attitudes in support of adaptive pathways ( [[#Laspidou--2014|Laspidou, 2014]] ).

ICTs play a role in adaptive responses to both short-term shocks and long-term trends associated with climate change. Timely access to information (e.g., early warning, temperature and rainfall, agricultural advice) through ICTs (e.g., mobile devices, SMS, radio, social media) can be crucial to respond and mitigate the impact of emergencies such as floods and drought, for identifying pest and disease prevalence, and for informing livelihood options, key in adaptation pathways of vulnerable communities ( [[#Devkota--2018|Devkota and Phuyal, 2018]] ; Panda et al., 2019).

In addition to contributing to the robustness and stability of the critical infrastructure in the event of disasters, ICTs can strengthen other attributes of resilient urban systems by enabling learning and community self-organisation, cross-scale networks and flexibility, helping vulnerable stakeholders, in particular, to adjust to change and uncertainty ( [[#Heeks--2015|Heeks and Ospina, 2015]] ; [[#Heeks--2019|Heeks and Ospina, 2019]] ). Big data is being used to inform responses to humanitarian emergencies (Pham et al., 2014; Ali et al., 2016), as well as to generate new forms of citizen engagement and reporting (e.g., community-based maps of flood-prone areas) that can help to inform coping and adaptive responses (Ogie et al., 2019).

The selection and use of ICTs for adaptation needs to be fairly grounded in the broader socio-cultural, economic, political and institutional context, to ensure that these tools effectively help address existing, emerging and future adaptive needs. Typically, ICT is inadequate on its own to make a significant difference ( [[#Toya--2015|Toya and Skidmore, 2015]] ). The role of ICTs in adaptive pathways is influenced by the availability of locally relevant information (e.g., weather-based advisory messages, local market prices), the accessibility of information by all members of the community (e.g., using various text, audio and visual content, local languages, addressing gender-related exclusion, cost and digital competencies) and the applicability of information at the appropriate scale (local, regional or national), including data quality and verification ( [[#Namukombo--2016|Namukombo, 2016]] ; Haworth et al., 2018).

Information privacy and security, as well as the unintended impacts of ICTs on inequality, spread of misinformation and on widening existing gaps (e.g., due to poverty, gender and power differentials), can also constrain the contribution of ICTs to urban adaptation (Haworth et al., 2018; [[#Coletta--2017|Coletta and Kitchin, 2017]] ; [[#Leszczynski--2016|Leszczynski, 2016]] ) and are among the key challenges that need to be addressed in order to fully realise their potential.

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<span id="energy"></span>
==== 6.3.5.4 Energy ====

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A number of measures are available to adapt existing energy infrastructure to climate change. These typically involve changing engineering design codes and upgrading facilities to cope with new climatic conditions, building redundancy and robustness into systems, and preparation to ensure continued operation following extreme events. Adapting low carbon energy infrastructure improves its climate resilience whilst simultaneously delivering mitigation goals ( [[#Kemp--2017|Kemp, 2017]] ; Feldpausch-Parker et al., 2018), benefitting all other sectors (Dawson et al., 2018; [[#Pescaroli--2018|Pescaroli and Alexander, 2018]] ; Kong, Simonovic and Zhang, 2019).

[[#Hall--2019|Hall et al. (2019)]] identified 4223 GW of global power generation at risk of flooding. If these assets were protected by 0.5 m flood protection, ~700 GW would be at risk from the 1-in-100 year flood. Many assets can be strengthened, relocated or replaced with new equipment built to higher standards. An example of this is in the UK where a total of £172 million is being invested between 2011 and 2023 to raise flood protection of substations to be resilient to the 1-in-1000 year flood ( [[#ENA--2015|ENA, 2015]] ). Electricity cables can be upgraded in anticipation of reduced efficiency in a warmer climate, although in many locations this may be achieved autonomously to meet growth in electricity demand (Fu et al., 2017).

Fuels, including oil, natural gas, hydrogen, biomass and CO 2 prior to sequestration are delivered and distributed by pipeline or transportation by road, rail and shipping. In addition to engineering improvements, adaptation measures also include planning and preparation for service disruption by changing transport patterns, increasing local storage capacities and identifying and prioritising protection of critical transport nodes (Wang et al., 2019b; Panahi, Ng and Pang, 2020).

Several options are available to reduce the impacts of reduced cooling water for thermoelectric power generation, increases in water temperature and lower flows for hydropower generation. These include (i) switching from freshwater to seawater (if available) or air cooling; (ii) replacing once-through cooling systems with recirculation systems; (iii) replacing fuel sources for thermoelectric power generation; (iv) increasing the efficiency of hydro and thermoelectric power plants; (v) relaxing discharge temperature rules to allow warmer water to enter rivers; (vi) installation of screens to stop algae or jellyfish blooms clogging intakes; (vii) reducing power production and managing demand; and (viii) changing reservoir operation rules (where available). Shreshta et al. (2021) show that changing reservoir operation rules can offset reduced water availability under RCP8.5 until 2050, but is insufficient by the 2080s. van Vliet et al., (2016) showed that a 10% increase in hydroelectric generation efficiency can compensate for reduced water availability in most regions. Higher efficiency thermoelectric plans offset impacts under lower climate change scenarios but are shown to be inadequate under RCP8.5 by the 2080s; whereas a switch to seawater and dry (air) cooling provides a net increase under this scenario. However, these technologies can increase costs. Increasing the temperature of water discharged from the power station can have negative environmental impacts (Thome et al., 2016; Yang et al., 2015).

Longer term systemic strategies could include a combination of increased network redundancy and decentralisation of generation locations (Fu et al., 2017), or the use of ‘defensive islanding’ which involves splitting the network into stable islands to isolate components susceptible to failure and subsequently trigger a cascading event (Panteli et al., 2016). Smart grids are being increasingly deployed within municipalities to provide more efficient management of supply and demand and mitigate greenhouse gas emissions, however, there is limited understanding of their performance and reliability during floods and other extreme weather events (Vasenev, Montoya and Ceccarelli, 2016; Feldpausch-Parker et al., 2018).

Adaptation and preparedness at the household level can minimise impacts during power outages, but neighbourhood-level assistance may be more appropriate to ensure support for vulnerable households and coordination of action and information (Ghanem, Mander and Gough, 2016). More generally, it is important for responder organisations to integrate energy needs in disaster preparedness and response plans. Whilst over the longer term, reducing household and industrial demand for energy supply will reduce the need for capital investments and upgrades (Fu et al., 2017).

Providing a reliable and resilient power supply is crucial to economic and social development ( [[#Fankhauser--2016|Fankhauser and Stern, 2016]] ). Furthermore, there are co-benefits from the use of low carbon energy systems (Chapter 8, WGIII AR6). For example, solar-charged street lamps and household lighting gives reliable nighttime lighting, providing safety, security and resilience to disruption of network power supplies (Burgess et al., 2017). At larger scales, deploying solar power on building roofs reduces energy demand for cooling by 12% and lowers the urban heat island, and thereby has health benefits (Masson et al., 2014a). In the USA, construction of solar panels over 200 million parking spaces would generate a quarter of the country’s electricity supply ( [[#Erickson--2017|Erickson and Jennings, 2017]] ).

As presented in Table 6.3, access to energy supply varies considerably. In particular, many African countries require substantial energy infrastructure to support their economic development. The combination of smart technologies with solar and other renewable generation provides a huge opportunity (Anderson et al., 2017; [[#Kolokotsa--2017|Kolokotsa, 2017]] ). However, care must be taken in rapidly developing cities, as failure to ensure energy access during urbanisation can reduce resilience (Ürge-Vorsatz et al., 2018).

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<span id="transport-1"></span>
==== 6.3.5.5 Transport ====

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A wide range of adaptation options are available for transport infrastructure and most provide a good benefit cost ratio (Doll, Klug and Enei, 2014; Forzieri et al., 2018). Options include upgrading infrastructure (which can often be achieved autonomously as part of standard repair and replacement schedules) and strengthening or relocating (critical) assets. Adaptation of road and rail networks in Australasia includes re-routing, coastal protection, improved drainage and upgrading of rails (Table 11.7.) In areas with substantial infrastructure deficits, such as much of Africa, investments in public transport and transit-oriented development are highlighted as desired mitigation-adaptation interventions within cities of South Africa, Ethiopia and Burkina Faso ( [[IPCC:Wg2:Chapter:Chapter-9#9.8.5.3|Section 9.8.5.3]] ). Adapting low carbon transport infrastructure will be crucial to ensure resilience to climate change impacts whilst simultaneously delivering mitigation goals (Shaheen, Martin and Hoffman-Stapleton, 2019; Costa et al., 2018).

[[#Wright--2012|Wright et al. (2012)]] calculated that strengthening bridges in the USA would cost USD 140–250 billion by 2090 (or several billion dollars a year), but costs are reduced by 30% if interventions are made proactively. [[#Koks--2019|Koks et al. (2019)]] calculate a benefit–cost ratio of greater than one for over 60% of the world’s roads exposed to flooding. The greatest benefits from adaptation of the global road network are in LMICs where reductions in flood risk are typically between 40% and 80%. [[#Pregnolato--2017|Pregnolato et al. (2017)]] showed that in the city of Newcastle upon Tyne (UK), two carefully targeted interventions at key locations to manage surface water flooding reduced the impacts of the 1-in-50 year event in 2050 by 32%. In permafrost regions, geo-reinforcement, foundation and piles can be strengthened (Trofimenko, Evgenev and Shashina, 2017), whilst passive cooling methods, including high-albedo surfacing, sun-sheds and heat drains can cool infrastructure (Doré, Niu and Brooks, 2016).

[[#Hanson--2020|Hanson and Nicholls (2020)]] calculate the total global investment costs for port adaptation to sea level rise and provision of new areas at USD 223–768 billion by 2050. However, adaptation of existing ports is only 6% of this. [[#Yesudian--2021|Yesudian and Dawson (2021)]] estimate the cost of maintaining present levels of flood risk in 2100 for the global air network will cost up to USD 57 billion (Monioudi et al., 2018; Esteban et al., 2020b).

New technologies and design innovations can improve the resilience of cars, trains, boats and other vehicles to cope with more extreme weather. Mobility transitions have the potential to improve mobility and accessibility, to influence urban form and to reduce vehicular use (and thereby infrastructure degradation), vehicle miles travelled and vehicle-based emissions (Sperling, Pike and Chase, 2018). For example, use of electric vehicles, hydrogen vehicles and greater uptake of public transport and other vehicles that reduce exhaust head emissions reduces the urban heat island ( [[#Kolbe--2019|Kolbe, 2019]] ). Carsharing can reduce carbon emissions by over 50% (Shaheen, Martin and Hoffman-Stapleton, 2019). Ride hailing, matching non-professional drivers of private vehicles with paying passengers, positively impacts low-income, low-car ownership households in Los Angeles ( [[#Brown--2018|Brown, 2018]] ), and fills market gaps in cities where public transit infrastructure is inadequate, unreliable or unsafe (Suatmadi, Creutzig and Otto, 2019; [[#Vanderschuren--2018|Vanderschuren and Baufeldt, 2018]] ), but can also create a precarious and insecure job market that impacts well-being ( [[#Fleming--2017|Fleming, 2017]] ). Whether the resulting impacts are positive or negative, largely depends on local, national and international policy and practices.

Safe and convenient walking and cycling (and public transport) infrastructure in cities reduces carbon emissions and urban heat island intensity, but also improve cardiovascular capacity which reduces heat stress (Schuster et al., 2017). In some regions, warmer weather may bring opportunities for increased uptake of cycling and walking, though precipitation or thermal discomfort caused by high temperature and humidity can reduce the use of active travel modes for commuting and recreation ( [[#Chapman--2015|Chapman, 2015]] ). Shaded pavements and lanes, and measures to mitigate the urban heat island can reduce risks to disruption of active travel thereby also enhancing mitigation (Wong et al., 2017).

Full system re-design may enable the greatest resilience but it does not usually have a good benefit–cost ratio (Doll, Klug and Enei, 2014). Moreover, Caparros-Midwood et al. (2019) show that transport infrastructure planners will not always be able to resolve trade-offs between managing climate risks and mitigating greenhouse gases without tackling other sectors. However, infrastructure planners should continually seek opportunities for positive infrastructure lock in where available (Ürge-Vorsatz et al., 2018).

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<span id="water-and-sanitation-1"></span>
==== 6.3.5.6 Water and Sanitation ====

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Adaptation to water scarcity can be through measures to increase supply (e.g., water storage, rainwater harvesting, desalination, river basin transfers, increased abstraction, reduced pollution of water sources), or manage demand (e.g., reduce leakage lower consumption, use of water efficiency devices, greywater reuse, behaviour change). A combination of these measures is usually required (e.g., Ives, Simpson and Hall, 2018; Dirwai et al., 2021; Wang et al., 2018a). Reliable and well-adapted water and sanitation services support economic growth, public health, reduce marginalisation and poverty, and can lower energy use and improve water quality ( [[#Campos--2015|Campos and Darch, 2015]] ; [[#Miller--2017|Miller and Hutchins, 2017]] ; Jeppesen et al., 2015; Hamiche, Stambouli and Flazi, 2016).

Globally, water sector adaptation costs are estimated to be USD 20 billion yr -1 by 2050 (Fletcher, Lickley and Strzepek, 2019). Globally, the budget required by 2030 for water infrastructure (new and refurbishment) is more than half of the budget required for all infrastructure ( [[#Koop--2017|Koop and van Leeuwen, 2017]] ). For OECD countries, water adaptation increases costs by 2%, but this proportion is far higher for developing nations ( [[#Olmstead--2014|Olmstead, 2014]] ).

A number of adaptation actions are available to reduce the impacts of floods on water and sanitation infrastructure. Active management reduces blockages in water infrastructure and protects related services such as roads and culverts which are essential to ensure the operation of onsite sanitation infrastructure (Capone et al., 2020). The impact of floods for onsite or sewerage systems can be lowered by reducing or eliminating excreta from the environment through regular maintenance, cleaning and clearing of blockages ( [[#O’Donnell--2020|O’Donnell and Thorne, 2020]] ; Borges Pedro et al., 2020).

Infrastructure to protect key assets such as water and wastewater treatment plants or pumping stations has a high cost but benefits all connected households and reduces pollution from flood events. In well-regulated water sectors, there has been an increasing focus on such investments ( [[#Campos--2015|Campos and Darch, 2015]] ). Whereas more diffused cheaper interventions can reduce flood water ingress to domestic toilets (Irwin et al., 2018). [[#Luh--2017|Luh et al. (2017)]] found that protected dug wells were one of the least resilient technologies, whereas piped, treated, utility managed surface water systems had higher resilience.

Protecting water sources from pollution is even more important in a warmer climate that increases the frequency of algal blooms. Individual assets such as water intake pipes can be protected using screens (Kim et al., 2020a), whereas basin-scale land management is required to reduce nutrient load from runoff (Me et al., 2018), whilst injecting water or installing barriers can protect coastal aquifers from salinisation ( [[#Siegel--2020|Siegel, 2020]] ).

More radical structural interventions may be needed in the longer term, but would need to be planned and delivered in coordination with investments in other sectors, particularly housing (Lüthi, Willetts and Hoffmann, 2020). As an interim measure, sanitation services with a lower reliance on fixed infrastructure, or container-based sanitation could be appropriate in many urban areas that are badly affected by flooding (Mills et al., 2020).

Other actions include use of adaptive planning (Evans, Rowell and Semazzi, 2020), integration of measures of climate resilience into water safety plans (Prats et al., 2017), as well as improved accounting and management of water resources (Lasage et al., 2015). Policy prescriptions on technologies for service delivery and changes in management models offer potential to reduce risks, particularly in low-income settings (Howard et al., 2016). Where formal sewerage provision is lacking, community based adaptation that incorporates both the function of the sanitation system and the vulnerability of users (e.g., women, children, elderly, ill or disabled) into the design is essential ( [[#Duncker--2019|Duncker, 2019]] ).

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<span id="flood-management"></span>
==== 6.3.5.7 Flood Management ====

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Cities are deploying a broad range of strategies to adapt infrastructure to flooding, with hard engineering approaches (e.g., dikes and seawalls) increasingly complementing soft approaches, including planning and use of nature-based solutions, that emphasise natural and social capital ( [[#Jongman--2018|Jongman, 2018]] ; [[#Sovacool--2011|Sovacool, 2011]] ). The infrastructure can alter downstream risks and lead to increased residual risk by encouraging more floodplain construction (Miller, Gabe and Sklarz, 2019; [[#Ludy--2012|Ludy and Kondolf, 2012]] ). Physical infrastructure is highly cost effective for large settlements, but not always for small settlements (Tiggeloven et al., 2020) and can be inaccessible to poorer communities (Sayers, Penning-Rowsell and Horritt, 2018; Van Bavel, Curtis and Soens, 2018). It is often inflexible once installed but new designs and adaptive pathways are emerging (Anvarifar et al., 2016; [[#Kapetas--2020|Kapetas and Fenner, 2020]] ).

As urban areas have expanded, so too have the number of vulnerable assets, and efforts may now emphasise reducing construction in high-risk regions (Paprotny et al., 2018a). The National Flood and Coastal Erosion Risk Management Strategy for England, for example, calls for reductions in inappropriate developments in floodplains ( [[#Kuklicke--2016|Kuklicke and Demeritt, 2016]] ; [[#UK%20Environment%20Agency--2020|UK Environment Agency, 2020]] ). Because climate change increases the flood risk profile of certain regions, reconsideration of design criteria has become more common ( [[#Ayyub--2018|Ayyub, 2018]] ). New York City now requires the sewer system currently designed for hydraulic capacity in 5-year design life should be designed for 50-year design life, taking into account climate changes over that period ( [[#NYC--2019|NYC, 2019]] ).

Adaptation strategies are diverse and often involve hybrid physical and NBS, and increasingly integrated management plans that consider both flood prevention and designing infrastructure and supporting people to cope with floods when they occur. Adaptation typically focuses on (i) increasing the standard of protection to compensate for the increased magnitude of extreme events; (ii) increased maintenance to cope with increased frequency of extremes and changes in ambient conditions; (iii) changed maintenance regimes from narrower maintenance windows, for example as assets are used more frequently (Sayers, Walsh and [[#Dawson--2015|Dawson, 2015]] ); (iv) land use planning and management to reduce exposure and manage hydrological flows; and (v) raising awareness, preparedness and incident management. In high population areas, hard interventions such as dikes and levees are generally cost effective ( [[#Jongman--2018|Jongman, 2018]] ; Ward et al., 2017).

Prevention or attenuation solutions include: rooftop detention, reservoirs, bioretention, permeable paving, infiltration techniques, open drainage, floating structures, wet-proofing, raised structures, coastal defences, barriers and levees, and have been deployed in diverse configurations and environments around the world ( [[#Matos%20Silva--2016|Matos Silva and Costa, 2016]] ). Barcelona (Spain) reached 90% impermeable surface cover by the 1980s, and has recently begun implementing artificial detention, underground reservoirs and permeable pavement technologies ( [[#Favaro--2018|Favaro and Chelleri, 2018]] ; [[#Matos%20Silva--2016|Matos Silva and Costa, 2016]] ). Florida Power and Light (USA), which provides service to approximately 10 million people, is investing USD 3 billion in flood protection and the hardening of assets (for example, upgrading wooden poles to steel and concrete) (Brody, Rogers and Siccardo, 2019). The City of Seattle recommends increasing preventative maintenance activities, the regular review of appropriate pavement technologies and modifications to subgrades and drainage facilities for high-risk areas ( [[#City%20of%20Seattle--2017|City of Seattle, 2017]] ), whilst also providing benefits to transport disruption (Arrighi et al., 2019). Adaptation in African cities is often dominated by informal responses ( [[#Owusu-Daaku--2018|Owusu-Daaku and Diko, 2018]] ). In the absence of centralised responses, low-income residents in Nairobi (Kenya) dig trenches and construct temporary dikes to protect homes, and in Accra (Ghana) the community has developed a range of social responses, including communal drains and local evacuation teams, to help protect people and critical valuables, although these innovations require connection to city-wide infrastructure to effectively reduce widespread risk ( [[#Amoako--2018|Amoako, 2018]] ).

More recent developments include sensor arrays to catalogue a river’s reach and how changing hydraulics interact with roadways (Forbes et al., 2019). Kuala Lumpur’s (Malaysia) stormwater management and road tunnel (SMART) during extreme rain events transitions the motorway to a stormwater conduit, an example of multifunctionality enabling agility ( [[#Isah--2016|Isah, 2016]] ; Markolf et al., 2019). Smart stormwater control systems are starting to use real-time control to dynamically manage the retention and movement of water during storms, though uptake at large scales which provide the greatest improvements in performance have been limited (Xu et al., 2020b).

In contrast to a ‘fail-safe’ approach to design which emphasises strengthening infrastructure against more intense environmental conditions, ‘safe-to-fail’ flood strategies allow infrastructure to fail in its ability to carry out its primary function but control the consequences of the failure. Examples include the use of a bioretention basin in Scottsdale (Arizona, USA) to accommodate excess runoff and help drain the city; a subsidy for affected farmers for lost crop production as part of the Netherlands’ Room for the River programme; targeted destruction of a levee to control flooding in the Mississippi River Valley in 2011 (Kim et al., 2019). Water-sensitive urban design, low-impact development, sponge cities, sustainable urban drainage and natural flood management involve deployment of systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater to protect water quality and associated aquatic habitat. These are being designed and implemented at increasingly ambitious scales. For example, China’s Sponge City initiative sets a goal of 80% of urban land able to absorb or reuse 70% of stormwater through underground storage tanks and tunnels, and use of pervious pavements, in addition to NBS (Chan et al., 2018; [[#Muggah--2019|Muggah, 2019]] ). Similarly, several thousand water-sensitive urban design interventions have been implemented across the city of Melbourne (Kuller et al., 2018).

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<span id="coastal-management"></span>
==== 6.3.5.8 Coastal Management ====

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Physical coastal management infrastructure has significant benefits in reducing flood and erosion losses and damage from storms. Physical infrastructure includes seawalls, dikes, breakwaters, revetments, groynes and tidal barriers. Adapted infrastructure can alter risks in morphologically connected areas, and lead to increased residual risk by encouraging more construction in the coastal zone (Miller, Gabe and Sklarz, 2019; [[#Ludy--2012|Ludy and Kondolf, 2012]] ). The infrastructure is highly cost effective for large settlements, but not always for small settlements (Tiggeloven et al., 2020) and can be inaccessible to poorer communities (Fletcher et al., 2016; [[#Pelling--2019|Pelling and Garschagen, 2019]] ).

Anticipated costs for this vary widely. For example, [[#Hinkel--2014|Hinkel et al. (2014)]] calculate that adaptation costs to maintain current global levels of coastal flood protection would be 1.2–9.3% of gross world product but protect assets in human settlements of USD 21–210 billion; [[#Tiggeloven--2020|Tiggeloven et al. (2020)]] calculate the cost of adaptation to be USD 176 billion (although this would provide a benefit–cost ratio of 106 under RCP8.5); while [[#Nicholls--2019|Nicholls et al. (2019)]] estimate that global coastal protection would cost substantially more, up to USD 18.3 trillion between 2015 and 2100 for RCP8.5 (this includes ranges of unit costs and maintenance costs which have often been ignored).

Coastal protection infrastructure such as dikes and sluice gates can inhibit salinity intrusion through careful management of water levels, this can provide co-benefits for flood risk reduction and agricultural productivity, but can also have negative impacts on ecosystems (Renaud et al., 2015). Managed aquifer recharge can be effective if the objective is to secure freshwater drinking supply (Hossain, Ludwig and Leemans, 2018).

Physical infrastructure can provide substantial benefits, be constructed quickly and has enabled coastal cities and settlements around the world to flourish and grow. Multifunctional physical infrastructure can also provide economic and social co-benefits. These include integration of transport, recreation, agriculture (e.g., cattle pasture), founding for wind turbines, housing, office or industry into the coastal management infrastructure (Anvarifar et al., 2017; [[#Kothuis--2017|Kothuis and Kok, 2017]] ). However, physical infrastructures can also disrupt natural processes, often leading to undesirable impacts such as pollution, degradation of ecosystems and displacement of erosion and flood risk to other locations (Wang et al., 2018b; [[#Dawson--2015|Dawson, 2015]] ; Nicholls, Dawson and Day, 2015). Coastal management strategies that take a hybrid approach, integrating physical and natural infrastructure, provide the best opportunities for managing risk and achieving wider socioeconomic and environmental benefits ( [[#Depietri--2017|Depietri and McPhearson, 2017]] ; Morris et al., 2018; Schoonees et al., 2019; Powell et al., 2019).

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<span id="cross-cutting-themes"></span>
=== 6.3.6 Cross-Cutting Themes ===

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This section builds on 6.3.4 to offer two entry points for assessing urban adaptation that extend beyond individual infrastructure types and that demonstrate the interdependent and dynamic natures of urban systems.

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<span id="equity-and-justice"></span>
==== 6.3.6.1 Equity and Justice ====

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Questions of equity and justice influence adaptation pathways for cities, settlements and infrastructure (see also Chapter 8). Although infrastructure, ranging from social to ecological and physical to digital, can help to reduce the impacts of climate change ( [[#Stewart--2014|Stewart and Deng, 2014]] ; Baró Porras et al., 2021), there is ''limited evidence'' of how infrastructures, implemented to reduce climate risk, also reduce inequality. Rather, there is more evidence to suggest that both adaptation plans and associated infrastructure implementation pathways are increasing inequality in cities and settlements (Chu, Anguelovski and Carmin, 2016; Anguelovski et al., 2016; [[#Romero-Lankao--2019|Romero-Lankao and Gnatz, 2019]] ). Social, economic and cultural structures that marginalise people by race, class, ethnicity and gender all contribute in complex ways to climate injustices and need to be urgently addressed for adaptation options to shift to benefit those most vulnerable, rather than mainly benefitting the already privileged and maintaining the status quo (Thomas et al., 2019; Porter et al., 2020; [[#Ranganathan--2019|Ranganathan and Bratman, 2019]] ). Innovation and imagination are needed in adaptation responses to ensure that cities and settlements shift from perpetuating structural domination and inequality to fairer cities (Porter et al., 2020; [[#Henrique--2019|Henrique and Tschakert, 2019]] ; [[#Parnell--2016b|Parnell, 2016b]] ). To support these possibilities, this section explores adaptation through the lens of distributive and procedural justice. Although not expanded on here, spatial and recognition injustices are equally important ( [[#Fisher--2015|Fisher, 2015]] ; [[#Chu--2018|Chu and Michael, 2018]] ; Campello Torres et al., 2020). Recognition can be supported through a capabilities approach that helps to bring attention to past cultural domination and enable citizens to develop the functioning life they choose (Schlosberg, Collins and Niemeyer, 2017). This brings a focus on local action, emphasising the relevance to vulnerability reduction and resilience building of individual and local/community capacities and supporting structures. This blurs the distinction between climate change adaptation and community development, with the former firmly embedded in the latter. Struggles for recognition are deeply political and central to adaptation responses which requires increased focus on power to support more equitable and just adaptation ( [[#Nightingale--2017|Nightingale, 2017]] ). Justice questions are not static, Box 6.4 overviews the implications of COVID-19 for urban justice and vulnerability.

Distributive justice calls attention to unequal access to urban services, land, capital and technology. Related to this, exposure to health, flooding and drought risks of people living in low-income and informal settlements is a growing concern, as is disaster preparedness and the ability to support the needs of vulnerable groups such as the elderly, children and disabled, where data is often lacking (Lilford et al., 2016; Castro et al., 2017). There are also differences in who benefits from infrastructures, as they are inherently political, embedded in social contexts, politics and cultural norms ( [[#McFarlane--2017|McFarlane and Silver, 2017]] ) and often tend to benefit those already privileged ( [[#Henrique--2019|Henrique and Tschakert, 2019]] ). As an example, fixing water leaks can depend as much on the politics of who is involved and whose knowledge is prioritised as on the technical aspects ( [[#Anand--2015|Anand, 2015]] ).

The quality and maintenance of infrastructure is often unequal across cities, benefiting some and increasing vulnerability of others. Some property is seen as dangerous and of lower value if highly exposed to risk (Wamsley et al., 2015). Similarly, areas suffering from disinvestment in infrastructure might have a high risk of flooding ( [[#Haddock--2013|Haddock and Edwards, 2013]] ). Zoning and land use trade-offs have been seen to be unequally skewed in favour of prime real estate and economically valuable assets (e.g., protecting factories and refineries from flooding) (Anguelovski et al., 2016; Carter et al., 2015). Urban planning reforms are therefore central to building a fairer urban adaptation response ( [[#Parnell--2016b|Parnell, 2016b]] ).

Infrastructure is often not adequately implemented in low-income urban areas and not equally accessible to all (Meller et al., 2017). For example, low-income neighbourhoods often have less green space and therefore less associated cooling benefits. Even in high-income areas, there is often unequal access to services. For example, an assessment of sustainable urban mobility plans in Portugal showed that some areas have considered equity in their plans and increased access for disadvantaged users including the elderly and disabled, but in other cities this is lacking (Arsenio, Martens and Di Ciommo, 2016). Understanding who has access to what infrastructure can help to redress the drivers of social vulnerability that are central to just urban adaptation (Michael, Deshpande and Ziervogel, 2018; Shi et al., 2016).

Changing land use and increasing green spaces to reduce climate risks and attract investments and job opportunities has increased real estate values, triggered climate gentrification in some areas (Keenan, Hill and Gumber, 2018) and decreased access to affordable housing in other areas ( [[#Larsen--2015|Larsen, 2015]] ; Carter et al., 2015). Displacement through evictions and relocations linked to land use conversion and resettlement in the name of adaptation has also increased people’s vulnerability (Anguelovski et al., 2016; [[#Henrique--2019|Henrique and Tschakert, 2019]] ).

Understanding social and economic elites and their investment in infrastructure has implications for distributive justice, particularly when there is secession from public infrastructure services that has financial implications for viability (Romero-Lankao, Gnatz and Sperling, 2016). In the case of the 2015–17 Cape Town drought, wealthy households secured their water needs through off-grid technologies such as rainwater tanks and boreholes. Although this resulted in more water being available in the dams, it also led to less revenue being collected for municipal water and less ability to cross-subsidise water for poor households ( [[#Ziervogel--2019b|Ziervogel, 2019b]] ; [[#Simpson--2019|Simpson, 2019]] ; [[#Bigger--2019|Bigger and Millington, 2019]] ). More attention needs to be paid to how shifts in infrastructure are serving the interests of urban elites, often driven by the state, and failing to adequately consider the needs of the disadvantaged (Bulkeley, Castán Broto and Edwards, 2014; [[#Ajibade--2017|Ajibade, 2017]] ; Shi et al., 2016). Equally, more risk-reducing infrastructure is needed across all urban areas (Reckien et al., 2018a).

Procedural justice, which focuses on the institutional processes by which adaptation decisions are made, brings attention to the lack of opportunity for engaging in political decision making and limited representation of diverse voices in cities and settlements, and in relation to investment in infrastructure ( [[#Coates--2020|Coates and Nygren, 2020]] ; [[#Henrique--2019|Henrique and Tschakert, 2019]] ). Even when inclusive adaptation processes are run, they seldom produce procedurally just outcomes ( [[#Malloy--2020|Malloy and Ashcraft, 2020]] ). Understanding who is excluded and included is important (Sara, Pfeffer and Baud, 2017). One example is the increasing numbers of migrants who are confronted with lack of access to citizenship rights and housing tenure ( [[#Romero-Lankao--2018|Romero-Lankao and Norton, 2018]] ). Often, migrants are not allowed to formally claim public provisions in health, finance and shelter ( [[#Chu--2018|Chu and Michael, 2018]] ). Further, migrants and their settlements are likely unrecognised in spatial or infrastructure development plans. In this context, social infrastructure, zoning and land use planning for climate adaptation has triggered inequity through omission, as some planning process have been racialised and excluded groups such as migrants and ethnic minorities (Anguelovski et al., 2016). Urban adaptation policy-making processes that explicitly integrate multiple stakeholder interests can help to balance top-down solutions (Reckien et al., 2018a).

Identifying who is least able to adapt to climate risks sufficiently is important (Thomas et al., 2019). Some people may have few opportunities to relocate away from flooded areas in the long term or to evacuate in the short term. It is also harder for many from low-income areas to rebuild after an extreme event. Lack of housing tenure and sub-standard housing has been shown to limit the ability of residents to improve and manage their landscapes and therefore it is hard for them to enhance energy efficiency (Dempsey et al., 2011). Access to information is critical for adapting to climate risk and reducing vulnerability to hazards, yet access to this information is often not equally available (Ma et al., 2014). For example, low literacy can hamper ability to respond to early warning information (Dugan et al., 2011). In other instances, racial violence has surfaced during disasters, with Black victims’ lives being seen as less important than others (Anderson et al., 2020).

When looking at justice issues in urban adaptation, it is important to recognise that the adaptation of one individual or household may lead to maladaptation and negative impacts elsewhere ( [[#Holland--2017|Holland, 2017]] ; Limthongsakul, Nitivattananon and Arifwidodo, 2017; [[#Atteridge--2018|Atteridge and Remling, 2018]] ). For example, the case of an area of peri-urban Bangkok experiencing localised flooding due to unregulated private sector development saw households take both individual (building flood walls around homes, digging temporary drainage swales in the carriageway) and collective action (petitioning authorities, pumping water into vacant land). These actions, to a certain extent, merely displaced the flood water to other areas, or created new problems by damaging the carriageway, creating negative impacts on other households and the wider community. However, ultimately, it was the actions of improperly regulated private sector developers driving the need for this autonomous adaptation (Limthongsakul, Nitivattananon and Arifwidodo, 2017).

One of the tensions that emerge when addressing injustice is that the global provision of modern infrastructure is increasingly seen as unfeasible. It is unfeasible, both in terms of the current high emissions associated with infrastructure ( [[#World%20Bank--2017|]] [[#World%20Bank--2017|World Bank, 2017]] ) and the centralised, high standard ideal (Lawhon, Nilsson and Silver, 2018; [[#Coutard--2015|Coutard and Rutherford, 2015]] ). Decentralisation is increasingly needed, which the urban poor already engage in through their use of ‘informal’ infrastructure technologies, given their limited access to infrastructure networks. Transformative adaptation pathways that reduce climate risk whilst reducing inequity require an approach that sees infrastructure as inherently social and political.

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<span id="mitigation-and-adaptation"></span>
==== 6.3.6.2 Mitigation and Adaptation ====

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As analytical concepts, mitigation and adaptation have helped, over the years, to structure thinking and action around climate change. However, since AR5 there has been a growing debate about the adequacy of a neat separation between adaptation and mitigation ( [[#Castán%20Broto--2017|Castán Broto, 2017]] ).

The delivery of climate change action has revealed numerous co-benefits between adaptation and mitigation, around diverse areas such as implementing NBS and delivering health and development benefits (Ürge-Vorsatz et al., 2014; Suckall, Stringer and Tompkins, 2015; [[#Puppim%20de%20Oliveira--2016|Puppim de Oliveira and Doll, 2016]] ; Spencer et al., 2017). There has been a strong interest in delivering development benefits alongside climate mitigation, thus benefiting the overall infrastructure base (Suckall, Stringer and Tompkins, 2015). Some of these co-benefits have also emerged in experiences of urban planning, pointing toward the dilemma of separating adaptation and mitigation in a context in which integration, rather than an analytical differentiation, was seen as being required to transcend work in silos ( [[#Aylett--2015|Aylett, 2015]] ). Because urban planning needs to carefully consider long time scales, the neat separation between mitigation and adaptation runs counter to integrated forms of planning that can consider scales (time and space) carefully and that are aimed to deliver the sustainable city as a whole (Solecki et al., 2015; Grafakos et al., 2020).

For example, the ideas of climate resilient development and climate compatible development help planners to consider the simultaneous wins that emerge between adaptation, mitigation and development, requiring institutional building and partnerships to deliver triple win solutions (Stringer et al., 2014; Seo, Jaber and Srinivasan, 2017; [[#Mitchell--2010|Mitchell and Maxwell, 2010]] ). While the evidence base for the actual possibility of achieving such triple wins remains scarce (Tompkins et al., 2013; [[#Sharifi--2020|Sharifi, 2020]] ), emerging examples show important developments. For example, establishing safe and convenient walking and cycling infrastructure can lead to improvements in population health, thereby highlighting the close interaction between urban land use, infrastructure and population health (Schuster et al., 2017), while clean cooking has the potential to deliver positive health outcomes alongside improvements in air quality and emissions reductions and through reducing pressure on woodland as a fuel source for expanding urban populations ( [[#Msoffe--2017|Msoffe, 2017]] ). Furthermore, active transport infrastructure reduces air pollution and related health risks, and helps to mitigate further climate change (Schuster et al., 2017). These are supported by city networks such as the C40 Clean Air Cities Declaration and the Clean Air Coalition that complements WHO guidelines and standards, for example through the Breathe Life Campaign. In conclusion, in both urban environments and infrastructural sectors, triple wins are only realisable through broader perspectives that link climate compatible development to institutional change or the achievements of wider welfare objectives such as those enshrined in the United Nations 2030 Agenda of Development (Castán Broto et al., 2015; England et al., 2018) ( ''medium evidence'' , ''high agreement'' ).

The aspiration to deliver climate change action within a broader agenda of transformative change, introduced in the SREX report, received renewed attention after the publication of IPCC Special Report on Global Warming of 1.5°C, which argues for a focus on urban transformations and highlighted that informal settlements were vital for understanding the delivery of these transformations. Deep decarbonisation has emerged as a new idea that regards the development of low or zero carbon pathways as a condition for good adaptation in the long term. Decarbonisation becomes urgent in the face of growing impacts attributable to climate change (Ribera et al., 2015; Bataille et al., 2016; Wesseling et al., 2017). Urbanisation opens opportunities for deep mitigation in low-impact developments, and hence, it is imperative to understand the implications of those opportunities for climate action ( [[#Mulugetta--2018|Mulugetta and Broto, 2018]] ). These gains are not limited to urban areas. The reliance on connected urban–rural systems for water, food and fuel has led to city government and urban-based businesses supporting landscape adaptations in rural hinterlands with strong potential for mitigation and rural development co-benefits. Water Funds bring downstream urban public and private finance to support upstream rural residents to make land use and agricultural management decisions to avoid damaging runoff, soil erosion and downstream sedimentation with reduction in water quality and increased flood risk. There are more than 30 Water Funds in Latin America and sub-Saharan Africa. These operate at landscape scale; the Upper Tana-Nairobi Water Fund, Kenya (Vogl et al., 2017), planned for a USD 10 million investment in Water Fund-led conservation interventions, with a projected return of USD 21.5 million in economic benefits over a 30-year timeframe ( [[#Apse--2015|Apse and Bryant, 2015]] ). However, these investments do not occur where communities lack funding or the institutions to direct funding from downstream beneficiaries to upstream residents (Brauman et al., 2019).

<div id="box-6.4" class="h2-container box-container"></div>

'''Box 6.4 | Adapting to Concurrent Risk: COVID-19 and Urban Climate Change'''
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COVID-19 impacts have highlighted the depth and unevenness of systemic social vulnerability and the compounding characteristics of contemporary development models, with direct relevance to climate change risk accumulation and its reduction (Patel et al., 2020b; [[#Manzanedo--2020|Manzanedo and Manning, 2020]] ; [[#Bahadur--2020|Bahadur and Dodman, 2020]] ). This is plain at the global level: of the estimated 119–124 million additional people induced into poverty by COVID-19 in 2020, South Asia and sub-Saharan Africa each contribute two-fifths (Lakner et al., 2021). These are rapidly urbanising and highly climate-hazard-exposed world regions, indicating COVID-19 impacts may further concentrate risk in these regions. Within cities, COVID-19 and climate change risk and loss is concurrent by gender, race and income or livelihood, for example, when vulnerable elderly populations are simultaneously exposed to COVID-19 and heatwave risk. Globally, in 2020, about 431.7 million vulnerable people were exposed to extreme heat during the COVID-19 pandemic, including about 75.5 million during the July and August 2020 European heatwave, with an excess mortality of over 9000 people arising from heat exposure ( [[#Walton--2020|Walton and van Aalst, 2020]] ).

The pandemic has demonstrated the multiple, often reinforcing, ways in which specific drivers of vulnerability interact both in generating urban risk and shaping who is more or less able to recover (Phillips et al., 2020; Honey-Rosés et al., 2020) (see [[#6.2|Section 6.2]] ). Again, this is not a new lesson for urban climate change adaptation, but it is a lesson that has not yet been seen to enter into routine practice for urban adaptation. Two key challenges for climate change adaptation are the associations between COVID-19 risk and urban connectivity and overcrowding. Connectivity has been presented in urban adaptation policy as a virtue, a means to share risk and diversity inputs (Ge et al., 2019; [[#Kim--2020|Kim and Bostwick, 2020]] ), COVID-19 has surfaced the unevenness with which people and places are connected and also the need to balance connectivity against risk transfer, through the failure of food supply chains or remittance flows, as well as by the direct transfer of disease (Challinor et al., 2018). High-density living has advantages for urban resource efficiency including benefiting climate change mitigation. When high-density living is not supported by adequate access to critical infrastructure (sufficient internal living space, access to potable water and sanitation, access to open green space), this exacerbates overcrowding and generates vulnerability to multiple risks, including climate change hazards and communicable disease (Bamweyana et al., 2020; Hamidi, Sabouri and Ewing, 2020; [[#Peters--2020|Peters, 2020]] ; Satterthwaite et al., 2020). Where overcrowding coincides with precarious livelihoods, for example in informal settlements, risk is further elevated ( [[#Wilkinson--2020|Wilkinson, 2020]] ). Neighbourhood associations (a benefit of high-density living) have been an important source of resilience through providing trusted information, access to food and water for washing during the pandemic and serving populations unable to access government or market provision (Pelling et al., 2021). Here local organising has not only met gaps in service provision, but opened dialogue to vision and organise for alternative development futures. These distinctly urban challenges should be read as a sub-set of wider cross-cutting lessons for recovery from COVID-19 (see Cross-Chapter Box COVID in Chapter 7).

Where responses to COVID-19 include addressing inequities in social infrastructure, this opens a considerable and potentially society-wide opportunity to reduce social vulnerability to climate change risks (see Cross-Chapter Box COVID in Chapter 7).

<div id="6.3.7" class="h2-container"></div>

<span id="climate-resilient-development-pathways"></span>
=== 6.3.7 Climate Resilient Development Pathways ===

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Table 6.6 represents the contribution of 21 adaptation measures identified in this chapter to 17 components of climate resilient development (CRD). CRD brings together the aims of climate adaptation, climate mitigation, sustainable development and social justice ( [[#Singh--2021|Singh and Chudasama, 2021]] ). This provides a first assessment of the viability of adaptation to cities, settlements and key infrastructure as a part of global transition to sustainability (see also Cross-Chapter Box FEASIB in Chapter 18).

'''Table 6.6 |''' Urban climate resilient development

{| class="wikitable"
|-
! colspan="2"| Adaption Measure

! Land-use planning 6.3.2.1

! Livelihoods and social protection 6.3.2.2

! Emergency management and security 6.3.2.3

! Health 6.3.2.4

! Education &amp; Comms. 6.3.2.5

! Cultural heritage &amp; institutions 6.3.2.6

! Temp. regulation 6.3.3.1

! Air quality regulation 6.3.3.2

! Stormwater and sanitation 6.3.3.3

! Coastal flood protection 6.3.3.4

! Riverine flood impact reduction 6.3.3.5

! Water provisioning and management 6.3.3.6

! Food production and security 6.3.3.7

! Built form 6.3.4.1

! Housing and building design 6.3.4.2

! ICT 6.3.4.3

! Energy Inf. 6.3.4.4

! Transport 6.3.4.5

! Water and sanitation 6.3.4.6

! Flood management 6.3.4.7

! Coastal management 6.3.4.8

|-
! colspan="2"| Inf. Systems

! colspan="6"| Social Inf.

! colspan="7"| Nature based solutions

! colspan="8"| Grey/Physical Inf.

|-
| rowspan="2"| Transformation towards sustainable development (human systems fundamental change + impact on wider system)

| Ecological transformation

| HA-ME

| LA-LE

| MA-ME

| LA-LE

| MA-RE

| HA-RE

| HA-ME

| MA-LE

| MA-ME

| MA-ME

| MA-ME

| HA-ME

| MA-ME

| MA-ME

| MA-ME

| LA-LE

| LA-LE

| LA-LE

| HA-RE

| MA-LE

| MA-LE

|-
| Social transformation

| HA-ME

| MA-ME

| MA-ME

| LA-LE

| HA-ME

| HA-RE

| LA-LE

| LA-LE

| LA-LE

| MA-LE

| LA-LE

| HA-LE

| HA-ME

| LA-LE

| MA-ME

| MA-ME

| LA-LE

| LA-LE

| LA-LE

| LA-LE

| LA-LE

|-
| rowspan="2"| Equity benefits

| Inclusive and locally accountable

| HA-ME

| MA-RE

| MA-ME

| MA-ME

| MA-ME

| HA-ME

| MA-LE

| MA-LE

| MA-LE

| LA-LE

| MA-LE

| MA-LE

| MA-LE

| LA-LE

| MA-ME

| LA-ME

| MA-ME

| MA-ME

| MA-ME

| LA-ME

| LA-ME

|-
| Targets poverty and marginality

| MA-LE

| HA-ME

| MA-ME

| HA-RE

| MA-ME

| MA-LE

| MA-LE

| LA-LE

| MA-LE

| MA-LE

| LA-ME

| LA-LE

| MA-ME

| LA-LE

| MA-ME

| LA-ME

| MA-ME

| MA-ME

| MA-RE

| MA-ME

| MA-ME

|-
| Contribution to GHG emission reduction

| Mitigation cobenefit

| HA-RE

| LA-LE

| HA-ME

| MA-ME

| HA-ME

| MA-LE

| HA-RE

| HA-ME

| HA-ME

| MA-ME

| HA-RE

| HA-ME

| MA-ME

| MA-ME

| MA-ME

| MA-ME

| HA-RE

| MA-LE

| HA-ME

| HA-LE

| HA-LE

|-
| rowspan="4"| Potential effectiveness

| Economic feasibility

| HA-RE

| MA-ME

| HA-ME

| MA-ME

| LA-LE

| HA-ME

| HA-ME

| MA-ME

| HA-ME

| HA-ME

| LA-ME

| HA-RE

| HA-ME

| LA-LE

| MA-ME

| HA-ME

| MA-ME

| MA-ME

| MA-ME

| HA-RE

| HA-RE

|-
| Benefit to other inf. systems adaptation

| HA-ME

| HA-LE

| HA-ME

| MA-ME

| LA-LE

| MA-LE

| MA-ME

| MA-LE

| HA-ME

| HA-ME

| MA-ME

| MA-ME

| MA-ME

| LA-LE

| MA-LE

| HA-RE

| HA-RE

| MA-ME

| HA-RE

| HA-RE

| HA-RE

|-
| Deploy at scale

| HA-ME

| HA-ME

| MA-ME

| HA-RE

| MA-LE

| LA-LE

| HA-ME

| MA-ME

| MA-LE

| MA-LE

| MA-ME

| HA-ME

| HA-ME

| HA-RE

| HA-RE

| HA-ME

| MA-ME

| MA-ME

| MA-ME

| HA-RE

| HA-RE

|-
| Flexibility post deployment

| HA-RE

| MA-ME

| MA-ME

| MA-ME

| HA-ME

| MA-ME

| MA-LE

| HA-ME

| MA-ME

| HA-LE

| MA-LE

| MA-ME

| MA-ME

| HA-RE

| HA-RE

| HA-RE

| HA-ME

| HA-ME

| HA-ME

| HA-ME

| HA-ME

|-
| Benefits to ecosystem services

| Ecological

| HA-RE

| LA-LE

| HA-ME

| MA-ME

| HA-LE

| MA-LE

| HA-ME

| MA-ME

| HA-ME

| HA-ME

| HA-RE

| HA-RE

| HA-ME

| MA-ME

| LA-LE

| LA-LE

| LA-LE

| LA-LE

| HA-RE

| MA-ME

| MA-ME

|-
| rowspan="3"| Benefits to Human

| Health

| HA-RE

| HA-LE

| HA-ME

| HA-RE

| HA-ME

| HA-ME

| HA-ME

| HA-ME

| HA-LE

| HA-LE

| HA-ME

| HA-ME

| MA-ME

| HA-RE

| HA-RE

| LA-LE

| LA-LE

| LA-LE

| HA-RE

| HA-RE

| HA-RE

|-
| Livelihood

| HA-RE

| HA-ME

| HA-ME

| HA-ME

| HA-ME

| MA-RE

| HA-ME

| MA-ME

| MA-LE

| MA-RE

| LA-ME

| MA-ME

| MA-ME

| MA-ME

| MA-ME

| HA-ME

| HA-RE

| HA-RE

| HA-RE

| HA-RE

| HA-RE

|-
| Social capital

| HA-RE

| HA-LE

| HA-ME

| HA-ME

| HA-RE

| MA-ME

| HA-ME

| HA-ME

| MA-ME

| MA-LE

| HA-ME

| MA-LE

| MA-ME

| LA-LE

| LA-LE

| HA-RE

| HA-LE

| HA-LE

| HA-LE

| MA-ME

| MA-ME

|-
| rowspan="4"| Risk coverage

| Transfer risk or impact to other people or places

| HA-RE

| HA-LE

| HA-ME

| HA-ME

| MA-ME

| HA-ME

| LA-LE

| LA-LE

| HA-ME

| LA-LE

| HA-ME

| MA-LE

| LA-LE

| MA-LE

| MA-ME

| LA-LE

| LA-LE

| LA-LE

| LA-ME

| HA-RE

| HA-RE

|-
| Reduces new hazard exposure generated

| HA-RE

| HA-ME

| MA-ME

| HA-ME

| MA-ME

| MA-LE

| LA-LE

| MA-LE

| MA-LE

| HA-LE

| MA-ME

| MA-LE

| MA-LE

| HA-RE

| HA-RE

| LA-LE

| LA-LE

| LA-LE

| MA-ME

| HA-ME

| HA-ME

|-
| Systemic vulnerability reduction

| HA-RE

| HA-RE

| MA-ME

| HA-RE

| MA-ME

| MA-ME

| LA-ME

| MA-LE

| MA-ME

| MA-ME

| MA-ME

| MA-LE

| HA-ME

| HA-RE

| HA-RE

| HA-ME

| HA-ME

| HA-ME

| HA-LE

| HA-ME

| HA-ME

|-
| Multi-climate Hazard

| HA-RE

| HA-ME

| HA-ME

| HA-RE

| HA-ME

| HA-ME

| HA-RE

| HA-ME

| HA-ME

| HA-ME

| HA-RE

| HA-RE

| HA-ME

| HA-RE

| HA-RE

| HA-RE

| HA-RE

| HA-RE

| HA-RE

| HA-RE

| HA-RE

|}

Key:

Climate Resilient Development Contribution

{| class="wikitable"
|-
|
| Negative

High

|
| Negative

Moderate

|
| Negative

Small

|
| Neglible

negative

|
| Nil

|
| Positive

Neglible

|
| Positive

Small

|
| Positive

Moderate

|
| Positive

High

|
| No

data

|}

Confidence

{| class="wikitable"
|-
| HA-

LE

| ''High''

''agreement –''

''limited''

''evidence''

| HA-

ME

| ''High''

''agreement –''

''medium''

''evidence''

| HA-

RE

| ''High''

''agreement –''

''robust''

''evidence''

| MA-

LE

| ''Medium''

''agreement –''

''limited''

''evidence''

| ME-

ME

| ''Medium''

''agreement –''

''medium''

''evidence''

| MA-

RE

| ''Medium''

''agreement –''

''robust''

''evidence''

| LA-

LE

| ''Low''

''agreement –''

''limited''

''evidence''

| LA-

ME

| ''Low''

''agreement –''

''medium''

''evidence''

| LA-

RE

| ''Low''

''agreement –''

''robust''

''evidence''

|}

Overall confidence: ''Medium agreement—medium evidence.'' Supplementary Material provides a detailed analysis including definitions for each component of climate resilient development and for each of the 357 entries an underlying explanatory statement linked to key evidence. Analysis was by [https://www.ipcc.ch/report/ar6/wg2/chapter/chapter-6 Chapter 6] Lead and Contributing Authors.

Two overarching messages and one key consequence for planning arise from Figure 6.4. First, urban adaptation measures can offer a considerable contribution to CRD. Second, this potential is realised by adaptations that extend predominant physical infrastructure approaches to also deploy nature-based solutions and social interventions. The consequence for planning is support for comprehensive monitoring and joined-up evaluation across the multiple components of CRD, as well as between the sectors that contribute to adaptation.

Table 6.6 shows that adapting key grey/physical infrastructure (built form and design, ICT, energy, transport, water and sanitation) is fundamental to CRD. This provides resilience to a range of hazards, with benefits to livelihoods, social capital and health, and provides benefits for the adaptation of other, connected infrastructure systems. Challenges to the contributions of grey/physical infrastructure, where adaptation through nature-based solutions and social policy offer alternatives are a lack of flexibility post-deployment constraining ability to flex as climate and vulnerability change; risk transferred to other people/places, not resolved; negative ecological consequences; and ''limited evidence'' of targeting marginality and inequality.

The significance of a CRD lens for the evaluation of adaptation strategy can be seen in approaches to riverine and coastal flooding. This viewpoint brings physical (e.g., embankments and defenses), nature-based (e.g., mangrove stands) and social policy (livelihood and social protection) options together. The benefits of physical infrastructure interventions for strengthening existing livelihoods and protecting health, for being deployable at scale and supporting other infrastructures to adapt are recognised and set these against challenges including hazard generation and risk transfer, limited flexibility, ecological harm, carbon costs and an undermining of social inclusion and accountability. Final evaluations will be determined by individual contexts, raising the importance of comprehensive monitoring of existing urban systems adaptation interventions and their association with ongoing development processes and outcomes (see [[#6.4|Section 6.4]] ).

The most consistent limit for all urban systems infrastructure types is in risk transfer. Current adaptation approaches in cities, settlements and key infrastructure have a tendency to move risk from one sector or place to others. With the exception of social infrastructure, the observed contribution of adaptation to social transformation is also limited. There are consequences for equity and sustainability as the impacts of climate change increase, and implications for evaluation and planning to work across adaptation interventions and connect with social and environmental policy and practice.

<div id="6.4" class="h1-container"></div>

<span id="enabling-conditions-for-adaptation-action-in-urban-areas-settlements-and-infrastructure"></span>