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

=== 6.1.4 Global Urban Trends ===

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Since AR5, many cities and other settlements, particularly unplanned and/or informal in Asia and Africa, have continued to grow at rapid rates (van den Berg , Otto and Fikresilassie 2021). Elsewhere, in Latin America in particular, while growth is less rapid, inequality persists. As a result, cities and settlements are crucial both as sites of potential action on climate change, and sites of increased exposure to risk ( ''medium evidence, high agreement'' ) ''.''

Patterns and trends for urban population growth were described in detail in AR5. Between 2015 and 2020, urban populations globally have grown by more than 397 million people, with more than 90% of this growth taking place in less developed regions ( [[#UNDESA--2018|UNDESA, 2018]] ). The latest population projections from [[#UNDESA--2018|UNDESA (2018)]] reinforce the trends identified previously, with even higher estimates for global urban populations. The 2012 data used in AR5 projected a global urban population of 4984 million in 2030 and 6252 million in 2050; the 2018 revisions project 5167 million and 6680 million respectively. Particularly noteworthy is the higher projection provided for sub-Saharan Africa’s urban population: increasing from 596 million to 666 million in 2030, and from 1069 million to 1258 million in 2050. These figures highlight the continued trend toward larger urban populations, and the particular significance of this in areas which currently have relatively small proportions of their populations living in towns and cities; this is also true in some Small Island States (e.g., the Solomon Islands) (McEvoy et al., 2020). The proportion of the global urban population living in megacities (with populations of more than 10 million people) is expected to continue growing slowly (to 16% of the urban total, or 862 million people, living in 48 agglomerations) by 2035 ( [[#UNDESA--2018|UNDESA, 2018]] ). The size and form of these megacities presents particular challenges with climate change impacts, in areas including air quality (Baklanov, Luisa and Molina, 2016), flooding (Januriyadi et al., 2018), and temperature increase (Darmanto et al., 2019) (see [[#6.2.3|Section 6.2.3]] ).

While there are few analyses of urban trends at the global scale, an additional 2.5 billion people are projected to be living in urban areas by 2050, with up to 90% of this increase concentrated in the regions of Asia and Africa, particularly in India, China and Nigeria, where 35% of this urban growth is projected to occur ( [[#UNDESA--2018|UNDESA, 2018]] ). Growth rates are slowing down in North America, South America and Europe ( [[#UNDESA--2018|UNDESA, 2018]] ). Much global growth continues to outstrip the ability of governments or the private sector to plan, fund and provide for sustainable urban infrastructure and this is most marked in low-income and informal settlements (Angel et al., 2016). Rural migration as a driver of urbanisation is discussed in 6.2.4.3, and literature has documented the way urban expansion and the conversion of agricultural land is also driven by investment incentives and weak planning policies (Colsaet, Laurans and Levrel, 2018; [[#Woodworth--2017|Woodworth and Wallace, 2017]] ). At the same time, early evidence suggests that, at least in some locations, out-migration from cities occurred as a result of the COVID-19 pandemic (Rajan, Sivakumar and Srinivasan, 2020), but the evidence is not clear and in some cases may have increased migration to other megacities (Chow et al., 2021). There is also growing recognition that poor planning has exacerbated the concentrated of deprivation in specific locations, deepening a cycle of exclusion and marginalisation ( [[#UNDESA--2020|UNDESA, 2020]] ).

One critical element of global urban trends which has received growing attention is informality (see also Prieur-Richard, Walsh and Craig, 2019). Informality is one of the key defining features of cities and settlements in the Global South (see Annex II: Glossary; Banks, Lombard and Mitlin, 2020; [[#Myers--2021|Myers, 2021]] ; [[#UN-Habitat--2016c|UN-Habitat, 2016c]] ). In almost all nations in the Global South, more than half the urban workforce work in informal employment; the proportions are particularly high in South Asia (82% in informal employment) and sub-Saharan Africa (66%) (Chen, Roever and Skinner, 2016; [[#Chen--2014|Chen, 2014]] ). The term ‘informal settlement’ refers to urban settlements or neighbourhoods that developed outside the formal system that is meant to record land ownership and tenure and without meeting a range of regulations relating to planning and land use, built structures and health and safety. Informality is a broader concept than ‘slums’, which are usually defined using measures of housing quality, provision of services and overcrowding. While most countries do not generate formal statistics on the number of people living in informal settlements, UN Habitat provides regional and global estimates of the number of urban households that are ‘slum’ households and therefore likely to include most residents of informal settlements. These estimates suggest that there were 1034 million slum dwellers in 2018, including some 56% of the urban population in sub-Saharan Africa and more than 30% of the urban population of South Asia ( [[#UN-Habitat--2020|UN-Habitat, 2020]] ). Informality is particularly important in understanding climate risks and responses in cities and settlements, and also in relation to key infrastructure ( [[#Trundle--2020|Trundle, 2020]] ; Taylor et al., 2021).

Evidence since AR5 confirms that occupants of informal settlements are particularly exposed to climate events given low-quality housing, limited capacity to adapt, and limited or no risk-reducing infrastructure ( ''high confidence'' ) ( [[#Melore--2020|Melore and Nel, 2020]] ; Twinomuhangi et al., 2021; Satterthwaite et al., 2020; Patel et al., 2020a)(see [[#6.2|Section 6.2]] and case study). The impacts of COVID-19 are also increasingly impacting high-density informal and slum settlements where social distancing and access to water for handwashing are limited (Bhide, 2020; Pinchoff et al., 2021; Tagliacozzo, Pisacane and Kilkey, 2021; [[#Wilkinson--2020|Wilkinson, 2020]] ). This compounds pre-existing vulnerability to climate change associated hazards. Box 6.1 expands on trends in informality as part of global urbanism, peri-urbanisation and suburbanisation, with implications for the global distribution of climate risks and adaptive capacity.

Adaptation and related concepts of urban climate resilience are also concerns for the broader agenda of sustainable development (Wachsmuth, Cohen and Angelo, 2016). Urban areas can play a positive role in advancing sustainability, but the pace and scale of urban development can also undermine progress in SDGs ( [[#Barnett--2016|Barnett and Parnell, 2016]] ; Maes et al., 2019; Anarfi, Hill and Shiel, 2020) ( ''high confidence'' ). With careful planning, urbanisation can be a transformative force, enhancing equity and well-being through co-benefits and synergies between climate change adaptation, equitable urban development and mitigation ( ''medium evidence, medium agreement'' ) ( [[#Parnell--2016a|Parnell, 2016a]] ; Solecki et al., 2015; [[#Sharifi--2020|Sharifi, 2020]] ). Cities can be effective change agents when supported by networked local and national institutions, including professional bodies ( ''high confidence'' ) (Andonova, Hale and Roger, 2017; [[#Brandtner--2021|Brandtner and Suárez, 2021]] ; Heidrich et al., 2016; [[#Kern--2019|Kern, 2019]] ; [[#Farzaneh--2020|Farzaneh and Wang, 2020]] ). Low Emission Development Strategies (LEDS) have developed effective science–policy interactions to support energy-system, environmental and economic development planning strategies in the city of Shanghai, China ( [[#Farzaneh--2020|Farzaneh and Wang, 2020]] ). New literature is emerging about how adaptive changes at the urban level could integrate both far reaching rapid emission reduction and community protection in transformative ways ( [[#Wamsler--2018|Wamsler and Raggers, 2018]] ; [[#Rosenzweig--2018|Rosenzweig and Solecki, 2018]] ; [[#UN-Habitat--2020|UN-Habitat, 2020]] ; [[#Ziervogel--2019a|Ziervogel, 2019a]] ). There is an increasing consensus about the need for integrated governance of urban areas within and across regions, so that urban risk management and adaptation happen hand in hand with more general processes of transition toward more sustainable urban regions ( [[#Simon--2016|Simon, 2016]] ; [[#UN-Habitat--2020|UN-Habitat, 2020]] ).

Since AR5, there has also been increasing recognition of the contribution of diverse knowledges including local and Indigenous knowledge in contributing to the development and interpretation of urban relevant climate change data and policy for effective action (Klenk et al., 2017; Hosen, Nakamura and Hamzah, 2020; [[#Makondo--2018|Makondo and Thomas, 2018]] ). Indigenous and local knowledge inform coping strategies in urban adaptation planning and new directions for action (Nakashima, Krupnik and Rubis, 2018; Abudu Kasei, Dalitso Kalanda-Joshua and Tutu Benefor, 2019). Indigenous and local knowledge is also found to shape perceptions about urban climate risk awareness, its acceptable limits, causation and preferences for adaptation (see also Pyhälä et al., 2016 for a review; see Jaakkola, Juntunen and Näkkäläjärvi, 2018 for impacts on Indigenous peoples in the EU; Saboohi et al., 2019). Local perceptions about climate change in turn influence adaptation behaviours in settlements and urban communities (Lee et al., 2015; Larcom, She and van Gevelt, 2019). Engagement with Indigenous and local knowledge is an enabling condition for planning community-appropriate climate adaptation responses (Fernández-Llamazares et al., 2015). Urban decision making that includes Indigenous and local knowledge has co-benefits for addressing indigenous dispossession, historical inequities and marginalisation of indigenous values that occurred (Parsons et al., 2019; [[#Carter--2019|Carter, 2019]] ; Maldonado et al., 2016; Orlove et al., 2014; Pearce et al., 2015). Indigenous and local knowledge can help deliver culturally appropriate strategies and local choices for urban risk management through, for example community-based observation networks (Alessa et al., 2016), integrating ecosystem-based adaptation strategies in institutional structures (Nalau et al., 2018), using multiple evidence-based approaches (Tengö et al., 2014), and adopting forms of governance that centre Indigenous peoples in urban adaptation and decision making ( [[#Horn--2018|Horn, 2018]] ; Parsons, Fisher and Nalau, 2016).

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'''Box 6.1 | Planetary Urbanisation and Climate Risk'''
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The scale, reach and complexity of contemporary urbanisation compounds climate risks and conditions adaptation ( ''high confidence'' ) ( [[#Miller--2017|Miller and Hutchins, 2017]] ; Rosenzweig et al., 2018b). Urbanisation manifests as a heterogeneous and plural process with varied spatial manifestations ( [[#Oswin--2018|Oswin, 2018]] ) that extends beyond cities and settlements, defining actions elsewhere in what has been called ‘planetary urbanization’ ( [[#Brenner--2014b|Brenner, 2014b]] ). While the concept of planetary urbanisation is contested, for example for a predominantly Eurocentric focus ( [[#Vegliò--2021|Vegliò, 2021]] ), the concept has reflected human urbanisation as a mega-trend of urban expansion and landuse intensification ( [[#Capon--2017|Capon, 2017]] ; [[#Lauermann--2018|Lauermann, 2018]] ). Three dimensions of planetary urbanisation are currently shaping adaptation actions: the new forms and scales of urbanisation, the blurring of boundaries around clearly demarcated territories, and the fragmentation of the urban hinterland into units that serve productive functions for the reproduction of urban space under capitalism ( [[#Brenner--2017|Brenner and Schmid, 2017]] ).

Planetary scale urbanisation challenges current understandings of spatial settlements and how risk affects urban communities ( ''limited evidence, medium agreement'' ) (Ruddick et al., 2018). Massive urbanisation manifests in large agglomerations such as metropolitan areas and urban regions, conurbations with unique risk challenges, particularly when interacting with other drivers of vulnerability ( [[#Adetokunbo--2015|Adetokunbo and Emeka, 2015]] ; Maragno, Pozzer and Musco, 2021). Experiences of regional collaboration to scale adaptation to metropolitan areas have shown to be effective, particularly facilitating information and technology exchanges and institutional cooperation ( [[#Shi--2019|Shi, 2019]] ; [[#Lundqvist--2016|Lundqvist, 2016]] ), but may face challenges such as addressing administrative and fiscal requirements and enrolling local populations in a meaningful participation process ( [[#Shi--2019|Shi, 2019]] ). For example, the coordination of planning policies in the Vienna–Bratislava metropolitan region, further divided by an international border, demonstrates that institutional coordination alone is not sufficient to deliver effective spatial governance: instead, meaningful spatial policies required the involvement of multiple actors ( [[#Patti--2017|Patti, 2017]] ). In addition to institutional coordination, adaptation in rapidly urbanising areas requires understanding how these processes magnify risk and condition urban responses (see also [[#6.3|Section 6.3]] ).

Urban expansion processes affect human settlements everywhere, regardless of their size. Figure 6.1 represents a continuum of settlements from high- to low-density areas ( [[#Ward--2016|Ward and Shackleton, 2016]] ). Urban and rural areas are not always clearly differentiated ( [[#Brenner--2014a|Brenner, 2014a]] ; [[#Brenner--2017|Brenner and Schmid, 2017]] ). For example, in 2010/2011, drought-exacerbated wildfires across Russia’s agricultural hinterland not only led to increased air pollution in Moscow and other large cities in the region, it also disrupted global supply chains of wheat and caused skyrocketing global food prices (Zscheischler et al., 2018). Floods in Bangkok, Thailand in 2011 destroyed many foreign-owned factories, leading to a global shortfall in different types of IT equipment ( [[#Levermann--2014|Levermann, 2014]] ).

Rural areas provide ecosystem services that benefit cities directly, including through reducing hazards (runoff, and temperature) and through carbon storage, and can be maintained through urban markets and other inputs ( [[#Gebre--2019|Gebre and Gebremedhin, 2019]] ). Most urban areas extend into dispersive peri-urban areas where urban and rural land uses co-exist ( [[#Simon--2016|Simon, 2016]] ) and/or suburban areas which are lower density and primarily residential in function. Moreover, the urban and rural differentiation creates normative expectations at the heart of planning conflicts and constraints of urban governance (Taylor, Butt and Amati, 2017). Expanding peri-urban areas pose specific structural constraints to addressing risks. In Bogotá, Colombia, a study found marked inequalities as more impoverished families had restricted access to peri-urban forests, trees and tree services (Escobedo et al., 2015). Factors such as limited land ownership and tenure insecurity in peri-urban areas hinder people’s ability to invest in permanent infrastructure to buffer themselves from flood events, as witnessed in the slums in Nairobi (Thorn, Thornton and Helfgott, 2015). Building resilience and adaptation via community mobilisation may not be effective in peri-urban areas shaped by migration, agricultural intensification and industrialisation ( [[#Wandl--2017|Wandl and Magoni, 2017]] ).

At the same time, actions to improve access to peri-urban services almost always improve resilience ( [[#Simon--2016|Simon, 2016]] ) Evidence from Kampala, Addis Ababa, Dar es Salaam, Douala, Ibadan, Nairobi, Dakar and Accra shows that urban and peri-urban agriculture and forestry can support adaptation (Lwasa et al., 2014). In the metropolitan area of Milan, multi-functional agriculture supports a local, more sustainable food chain ( [[#Magoni--2017|Magoni and Colucci, 2017]] ). Since communities in peri-urban areas are often transitory, efforts toward creating social capital by promoting civic engagement are crucial to facilitate collective action (Narain et al., 2017). For example, adaptation actions can help to build the capacity of the community to engage with service providers (Harris, Chu and Ziervogel, 2018; Ziervogel et al., 2017), as demonstrated in parts of peri-urban Kolkata, India and Khulna, and Bangladesh ( [[#Gomes--2018|Gomes and Hermans, 2018]] ; Gomes, Hermans and Thissen, 2018).

Urbanisation on an immense scale blurs the boundaries that previously defined cities and settlements ( [[#Arboleda--2016a|Arboleda, 2016a]] ; [[#Shaw--2015|Shaw, 2015]] ; [[#Brenner--2014a|Brenner, 2014a]] ; [[#OECD%20and%20European%20Commission--2020|OECD and European Commission, 2020]] ; [[#Schmid--2018|Schmid, 2018]] ; Davidson et al., 2019; [[#Wu--2020|Wu and Keil, 2020]] ). For example, peri-urban areas typically extend over multiple government jurisdictions ( [[#Wandl--2017|Wandl and Magoni, 2017]] ). Adaptation actions can be difficult to plan, coordinate, implement and evaluate in these transboundary contexts (Solecki et al., 2018; [[#Srivastava--2020|Srivastava, 2020]] ; [[#Fünfgeld--2015|Fünfgeld, 2015]] ; [[#Rukmana--2020|Rukmana, 2020]] ; Carter et al., 2018). In Medellín, Colombia, a 46-mile-long green belt is being built to stop urban expansion while also protecting urban forests, providing access to green spaces, and reducing urban heat island effects (Anguelovski et al., 2016). However, large-scale infrastructure projects such as this one require coordination between regional transport authorities and the different municipalities in charge of housing and public services, in addition to consulting communities on their social impact (Chu, Anguelovski and Roberts, 2017). Local and regional authorities have competing mandates, such as a competition for taxpaying residents in peri-urban, commuting zones, and different infrastructure investment logics, political drivers and constituent needs. Smaller discrete infrastructure projects that actively engage local populations may provide better opportunities to build resilience across fragmented spaces ( [[#Santos--2017|Santos, 2017]] ; [[#Kamalipour--2020|Kamalipour and Dovey, 2020]] ).

Suburbanisation follows a gradual movement of citizens from high-density urban centres to the suburbs ( [[#Pieretti--2014|Pieretti, 2014]] ). The development of enclaves for higher-income people that appropriate resources and constrain access to those resources for disadvantaged populations has been recorded in places as distant as Santiago de Chile, People’s Republic of China, India, Indonesia and the Philippines (Calvet and Castán Broto, 2016; Phelps, Miao and Zhang, 2020; Bulkeley, Castán Broto and Edwards, 2014; Buchori et al., 2021; [[#Kleibert--2018|Kleibert, 2018]] ). The appropriation of land and resources in enclaves defends exclusive, privileged communities at the expense of everyone else. Enclaves exacerbate inequalities because those who cannot afford to live in the enclave suffer the fragmentation of public services, restrictions in access to resources, and greater exposure to climate risks ( [[#Hodson--2010|Hodson, 2010]] ; Haase et al., 2017). Moreover, suburbanisation is linked to the privatisation of public spaces and the decline of public infrastructures, collective spaces and green projects ( [[#Long--2019|Long and Rice, 2019]] ; North, Nurse and Barker, 2017). Climate gentrification, whereby vulnerable communities are displaced from urban areas with lower climate risks ( [[#UN-Habitat--2020|UN-Habitat, 2020]] ), reconfigures urban areas, for example, as higher-income populations move away from the city centres, as shown in North American cities that have already suffered climate-related impacts such as Miami, Philadelphia and New Orleans (Keenan, Hill and Gumber, 2018; Shokry, Connolly and Anguelovski, 2020; [[#De%20Koning--2020|De Koning and Filatova, 2020]] ; Aune, Gesch and Smith, 2020).

Urbanisation leads to the spatial fragmentation of the hinterland, divided alongside functional units to serve the demands of the capitalist urban economy ( [[#Brenner--2017|Brenner and Schmid, 2017]] ). Urbanisation is thus linked to new intensities of resource exploitation that threaten vulnerable land and ecosystems, as shown in the Amazon, and that extend across scales ( [[#Arboleda--2016b|Arboleda, 2016b]] ; [[#Wilson--2018|Wilson, 2018]] ). The fragmentation of the hinterland for extractivist purposes depletes ecosystem services and further exacerbates cascading risks ( ''high confidence'' ) ( [[#6.2.6|Section 6.2.6]] ).

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