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

=== 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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==== 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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==== 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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==== 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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==== 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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==== 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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==== 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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==== 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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