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8 Urban Areas
Coordinating Lead Authors: Aromar Revi (India), David E. Satterthwaite (UK)
Lead Authors: Fernando Aragón-Durand (Mexico), Jan Corfee-Morlot (USA/OECD), Robert B.R. Kiunsi (United Republic of Tanzania), Mark Pelling (UK), Debra C. Roberts (South Africa), William Solecki (USA)
Contributing Authors: Jo da Silva (UK), David Dodman (Jamaica), Andrew Maskrey (UK), Sumetee Pahwa Gajjar (India), Raf Tuts (Belgium)
Review Editors: John Balbus (USA), Omar-Dario Cardona (Colombia)
Volunteer Chapter Scientist: Alice Sverdlik (USA)
This chapter should be cited as: Revi , A., D.E. Satterthwaite, F. Aragón-Durand, J. Corfee-Morlot, R.B.R. Kiunsi, M. Pelling, D.C. Roberts, and W. Solecki, 2014: Urban areas. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 535-612.
Chapter 8 Urban Areas
Executive Summary
Urban climate adaptation can build resilience and enable sustainable development. {8.1, 8.2, 8.3}
Action in urban centers is essential to successful global climate change adaptation. Urban areas hold more than half the world’s population and most of its built assets and economic activities. They also house a high proportion of the population and economic activities most at risk from climate change, and a high proportion of global greenhouse gas emissions are generated by urban-based activities and residents (medium confidence, based on medium evidence, high agreement). {8.1}
Much of key and emerging global climate risks are concentrated in urban areas. Rapid urbanization and rapid growth of large cities in low- and middle-income countries have been accompanied by the rapid growth of highly vulnerable urban communities living in informal settlements, many of which are on land at high risk from extreme weather (medium confidence, based on medium evidence, high agreement). {8.2, 8.3, Tables 8-2, 8-3}
Cities are composed of complex inter-dependent systems that can be leveraged to support climate change adaptation via effective city governments supported by cooperative multilevel governance. This can enable synergies with infrastructure investment and maintenance, land use management, livelihood creation, and ecosystem services protection (medium confidence, based on limited evidence, medium agreement). {8.3, 8.4}
Urban adaptation action that delivers mitigation co-benefits is a powerful, resource-efficient means to address climate change and to realize sustainable development goals (medium confidence, based on medium evidence, high agreement). {8.4}
Urban climate change risks, vulnerabilities, and impacts are increasing across the world in urban centers of all sizes, economic conditions, and site characteristics. {8.2}
Urban climate change-related risks are increasing (including rising sea levels and storm surges, heat stress, extreme precipitation, inland and coastal flooding, landslides, drought, increased aridity, water scarcity, and air pollution) with widespread negative impacts on people (and their health, livelihoods, and assets) and on local and national economies and ecosystems (very high confidence, based on robust evidence, high agreement). These risks are amplified for those who live in informal settlements and in hazardous areas and either lack essential infrastructure and services or where there is inadequate provision for adaptation. {8.2, Table 8-2}
Climate change will have profound impacts on a broad spectrum of infrastructure systems (water and energy supply, sanitation and drainage, transport and telecommunication), services (including health care and emergency services), the built environment, and ecosystem services. These interact with other social, economic, and environmental stressors exacerbating and compounding risks to individual and household well-being (medium confidence, based on medium evidence, high agreement). {8.2}
Cities and city regions are sufficiently dense and of a spatial scale that they influence their local micro-climate. Climate change will interact with these conditions in a variety of ways, some of which will exacerbate the level of climate risk (high confidence, based on robust evidence, high agreement). {8.2}
Urban climate adaptation provides opportunities for both incremental and transformative development. {8.3, 8.4}
Urban adaptation provides opportunities for incremental and transformative adjustments to development trajectories toward resilience and sustainable development via effective multilevel urban risk governance, alignment of policies and incentives, strengthened local government and community adaptation capacity, synergies with the private sector, and appropriate financing and institutional development. Opportunities to do so are high in many rapidly growing cities where institutions and infrastructure are
Urban Areas Chapter 8
being developed, though there is limited evidence of this being realized in practice (medium confidence, based on limited evidence, high
agreement). {8.4}
Urban adaptation can enhance economic comparative advantage, reducing risks to enterprises and to households and communities
(medium confidence, based on medium evidence, high agreement). {8.3}
City-based disaster risk management with a central focus on risk reduction is a strong foundation on which to address increasing
exposure and vulnerability and thus to build adaptation. Closer integration of disaster risk management and climate change adaptation
along with the incorporation of both into local, subnational, national, and international development policies can provide benefits at all scales
(high confidence, based on medium evidence, high agreement). {8.3}
Ecosystem-based adaptation is a key contributor to urban resilience (medium confidence, based on medium evidence, high
agreement (among practitioners)). {8. 3}
Effective urban food-security related adaptation measures (especially social safety nets but also including urban and peri-urban
agriculture, local markets, and green roofs) can reduce climate vulnerability especially for low-income urban dwellers (medium
confidence, based on medium evidence, medium agreement). {8.3}
Good quality, affordable, well-located housing provides a strong base for city-wide climate change adaptation minimizing
current exposure and loss. Possibilities for building stock adaptation rest with owners and public, private, and civil society organizations
(high confidence, based on robust evidence, high agreement). {8.3, 8.4}
Reducing basic service deficits and building resilient infrastructure systems (water supply, sanitation, storm and waste water
drains, electricity, transport and telecommunications, health care, education, and emergency response) can significantly reduce
hazard exposure and vulnerability to climate change, especially for those who are most at risk or vulnerable (very high confidence,
based on robust evidence, high agreement). {8.3}
For most key climate change associated hazards in urban areas, risk levels increase from the present (with current adaptation) to
the near term but high adaptation can reduce these risk levels significantly. It is less able to do so for the longer term, especially
under a global mean temperature increase of 4°C. {Tables 8-3, 8-6}
Implementing effective urban adaptation is possible and can be accelerated. {8.4}
Urban governments are at the heart of successful urban climate adaptation because so much adaptation depends on local
assessments and integrating adaptation into local investments, policies, and regulatory frameworks (high confidence). {8.4}
Well governed cities with universal provision of infrastructure and services have a strong base for building climate resilience if
processes of planning, design, and allocation of human capital and material resources are responsive to emerging climate risks
(medium confidence, based on medium evidence, high agreement). {8.4}
Building human and institutional capacity for adaptation in local governments, including scope for reflecting on incremental and
transformative adaptation pathways, accelerates implementation and improves urban adaptation outcomes (high confidence,
based on medium evidence, high agreement). {8.4}
Coordinated support from higher levels of governments, the private sector, and civil society and horizontal learning through networks
of cities and practitioners benefits urban adaptation (medium confidence, based on medium evidence, medium agreement). {8.4}
Urban Areas Chapter 8
8.1. Introduction
8.1.1. Key Issues
Adaptation to climate change depends centrally on what is done in urban centers, which now house more than half the world’s population and concentrate most of its assets and economic activities (World Bank, 2008; UN DESA Population Division, 2012). As Section 8.4 emphasizes, this will require responses by all levels of government as well as individuals and communities, the private sector, and civil society. The serious impacts of extreme weather on many urban centers each year demonstrate some of the risks and vulnerabilities to be addressed (UNISDR, 2009; IFRC, 2010). Climate change will usually add to these and other risks and vulnerabilities. Urban policies also have major implications for mitigation, especially for future levels of greenhouse gas (GHG) emissions and for delivering co-benefits, as discussed in WGIII AR5. This chapter focuses on the possibilities for governments, enterprises, and populations to adapt urban centers to the direct and indirect impacts of climate change.
The level of funding needed for sound urban adaptation could exceed the capacities of local and national governments and international agencies (Parry et al., 2009; Brugmann, 2012). Much of the investment will have to come from individuals and households, communities, and firms through their decisions to address adaptation and resilience (Agrawala and Fankhauser, 2008; Fankhauser and Soare, 2013). This might suggest little role for governments, especially local governments. But whether these small-scale decisions by households, communities, and firms do contribute to adaptation depends in large part on what local governments do, encourage, support, and prevent—as well as their contribution to providing required infrastructure and services. An important part of this is the provision by local governments of appropriate regulatory frameworks and the application of building standards, to ensure that the choices made by individuals, households, and firms support adaptation and prevent maladaptation. For instance, land use planning and management have important roles in ensuring sufficient land for housing that avoids dangerous sites and protects key ecological services and systems (UN-HABITAT, 2011a).
In reviewing adaptation needs and options for urban areas, the documentation reviewed for this chapter points to two key conclusions. The first is how much the adaptive capacity of any city depends on the quality of provision and coverage of infrastructure and services; the capacities for investments and land use management; and the degree to which buildings and infrastructure meet health and safety standards. This capacity provides a foundation for city resilience on which adaptation can be built. There is little of this foundation in most urban centers in low-income and in many middle-income nations. The second conclusion is the importance of city and municipal governments acting now to incorporate climate change adaptation into their development plans and policies and infrastructure investments. This includes not only building that foundation of resilience (and its institutional, governance, and financial underpinnings) but also mobilizing new resources, adjusting building and land use regulations, and continuously developing the local capacity to respond. This is not to diminish the key roles of other actors. But it will fall to city and municipal government to provide the scaffolding and regulatory framework within which other stakeholders contribute
and collaborate. Thus, adaptation in urban areas depends on the competence and capacity of local governments and a locally rooted iterative process of learning about changing risks and opportunities, identifying and evaluating options, making decisions, and revising strategies in collaboration with a range of actors.
8.1.2. Scope of the Chapter
This chapter focuses on what we know about the potential impact of climate change on urban centers and their populations and enterprises (Section 8.2), what measures are being taken to adapt to these changes (and protect vulnerable groups) (Section 8.3), and what institutional and governance changes can underpin adaptation (Section 8.4). Both this and Chapter 9 highlight the multiple linkages between rural and urban areas that have relevance for adaptation. This chapter also overlaps with Chapter 10, especially in regard to infrastructure, although this chapter focuses on urban infrastructure and in particular the infrastructure that comes within the responsibilities or jurisdiction of urban governments.
This chapter draws its urban statistics from the United Nations Population Division (UN DESA Population Division, 2012). Urban centers vary from those with a few thousand (or in some nations a few hundred) inhabitants to metropolitan areas with more than 20 million inhabitants. There is no international agreement—and considerable national variation—in how urban areas are defined (UN DESA Population Division, 2012). The main differences are in how settlements with a few hundred up to 20,000 inhabitants are classified; depending on the country, some, most, or all of these may be classified as urban or rural. There are also differences in how urban boundaries are set. In some places, they encompass the urban built up area or the central urban core; in others, they go well beyond the built up area and include large areas devoted to agriculture (Satterthwaite, 2007).
The issue here is whether provision for adaptation includes “rural” populations living around urban centers and within urban jurisdictions. In addition, it is common for part of the workforce in larger urban centers to live outside the urban center and to commute—and this may include many that live in settlements designated as rural. There is also no agreed definition for what constitutes a city—although the term city implies an urban center with some economic, political, or cultural importance and would not be applied to most small urban centers.
8.1.3. Context: An Urbanizing World
In 2008, for the first time, more than half the world’s population was living in urban centers and the proportion continues to grow (UN DESA Population Division, 2012). Three-quarters of the world’s urban population and most of its largest cities are now in low- and middle- income nations. A comparison of Figures 8-1 and 8-2 highlights the increase in the number of large cities from 1950 to what is projected for 2025. UN projections suggest that almost all the increase in the world’s population up to 2050 will be in urban centers in what are currently low- and middle-income nations (see Table 8-1). Most of the gross domestic product (GDP) of most nations and globally is generated
Chapter 8 Urban Areas
in urban centers and most new investments have concentrated there (World Bank, 2008; Satterthwaite et al., 2010). Clearly, just in terms of the population, economic activities, assets, and climate risk they increasingly concentrate, adapting urban areas to climate change requires serious attention.
Most urbanization is underpinned by an economic logic. All wealthy nations are predominantly urbanized and rapid urbanization in low- and middle-income nations is usually associated with rapid economic growth (World Bank, 2008; Satterthwaite et al., 2010). Most of the world’s largest cities are in its largest economies (World Bank, 2008;
Figure 8-1 | Global and regional maps showing the location of urban agglomerations with 750,000-plus inhabitants in 1950 (derived from statistics in UN DESA Population Division, 2012).
≤1 million 1.1–2.5 million 2.6–5 million 5.1–10 million
10 million
Chapter 8 Urban Areas
and services, mostly in informal settlements (UN-HABITAT, 2003a; Mitlin and Satterthwaite, 2013). Much of the health risk and vulnerability to climate change is concentrated in these settlements (Mitlin and Satterthwaite, 2013). So this chapter is concerned not only with an adaptation deficit for, but also with a development deficit that is relevant to, this risk and vulnerability.
Many aspects of urban change in recent decades have been so rapid that they have overwhelmed government capacity to manage them.
Among the 611 cities with more than 750,000 inhabitants in 2010, 47 had populations that had grown more than 20-fold since 1960; in 120, the growth was more than 10-fold (statistics in this paragraph are drawn from data in UN DESA Population Division, 2012). The increasing concentration of the world’s urban population and its largest cities outside the highest income nations represents an important change. Over the 19th and 20th centuries, most of the world’s urban population and most of its largest cities were in its most prosperous nations. Now, urban areas in low- and middle-income nations have close to two-fifths
Major area, region, or country 1950 1970 1990 2010 Projected for 2030 Projected for 2050
Urban population (millions of inhabitants)
World 745 1352 2281 3559 4984 6252 More developed regions 442 671 827 957 1064 1127 Less developed regions 304 682 1454 2601 3920 5125 Least developed countries 15 41 107 234 477 860 Sub-Saharan Africa 20 56 139 298 596 1069 Northern Africa 13 31 64 102 149 196 Asia 245 506 1032 1848 2703 3310 China 65 142 303 660 958 1002 India 63 109 223 379 606 875 Europe 281 412 503 537 573 591 Latin America and the Caribbeana^69 163 312 465 585 Northern America 110 171 212 282 344 396 Oceania 8 14 19 26 34 40
Percent of the population in urban areas
World 29.4 36.6 43.0 51.6 59.9 67. More developed regions 54.5 66.6 72.3 77.5 82.1 85. Less developed regions 17.6 25.3 34.9 46.0 55.8 64. Least developed countries 7.4 13.0 21.0 28.1 38.0 49. Sub-Saharan Africa 11.2 19.5 28.2 36.3 45.7 56. Northern Africa 25.8 37.2 45.6 51.2 57.5 65. Asia 17.5 23.7 32.3 44.4 55.5 64. China 11.8 17.4 26.4 49.2 68.7 77. India 17.0 19.8 25.5 30.9 39.8 51. Europe 51.3 62.8 69.8 72.7 77.4 82. Latin America and the Caribbean 41.4 57.1 70.3 78.8 83.4 86. Northern America 63.9 73.8 75.4 82.0 85.8 88. Oceania 62.4 71.2 70.7 70.7 71.4 73.
Percent of the world’s urban population
World 100.0 100.0 100.0 100.0 100.0 100. More developed regions 59.3 49.6 36.3 26.9 21.4 18. Less developed regions 40.7 50.4 63.7 73.1 78.6 82. Least developed countries 2.0 3.0 4.7 6.6 9.6 13. Sub-Saharan Africa 2.7 4.1 6.1 8.4 11.9 17. Northern Africa 1.7 2.3 2.8 2.9 3.0 3. Asia 32.9 37.4 45.2 51.9 54.2 52. China 8.7 10.5 13.3 18.6 19.2 16. India 8.5 8.1 9.8 10.6 12.2 14. Europe 37.6 30.5 22.0 15.1 11.5 9. Latin America and the Caribbean 9.3 12.1 13.7 13.1 11.7 10. Northern America 14.7 12.6 9.3 7.9 6.9 6. Oceania 1.1 1.0 0.8 0.7 0.7 0.
Table 8-1 | Distribution of the world’s urban population by region, 1950–2010 with projections to 2030 and 2050. Source: Derived from statistics in United Nations (2012).
aChapter 26 on North America includes Mexico; in the above statistics, Mexico is included in Latin America and the Caribbean.
Urban Areas Chapter 8
of the world’s total population, close to three-quarters of its urban population, and most of its large cities. In 2011, of the 23 “mega-cities” (with populations over 10 million), only 5 were in high-income nations (two in Japan, two in the USA, one in France). Of the remaining 18, 4 were in China, 3 in India, and 2 in Brazil. But more than three-fifths of the world’s urban population is in urban centers with fewer than 1 million inhabitants and it is here that much of the growth in urban population is occurring.
Underlying these population statistics are large and complex economic, social, political, and demographic changes, including the multiplication in the size of the world’s economy and the shift in economic activities and employment structures from agriculture to industry and services (and within services to information production and exchange) (Satterthwaite, 2007). One of the most significant changes has been the growth in the size and importance of cities whose economies increased and changed as a result of globalization (Sassen, 2012). Another is the number of large cities that are now centers of large extended metropolitan regions.
One of the challenges for this chapter is to convey the very large differences in adaptive capacity between urban centers. There are tens of thousands of urban centers worldwide with very large and measurable differences in population, area, economic output, human development, quality, and coverage of infrastructure and services, ecological footprint, and GHG emissions. The differences in adaptive capacity are far less easy to quantify. Table 8-2 illustrates differences in adaptive capacity and factors that influence it. It indicates how each urban center falls within a spectrum in at least four key factors that influence adaptation: local government capacity; the proportion of residents served with risk- reducing infrastructure and services; the proportion living in housing built to appropriate health and safety standards; and the levels of risk from climate change’s direct and indirect impacts. This chapter and Table 8-2 also draw on detailed case studies to illustrate this diversity—New York (Solecki, 2012), Durban (Roberts and O’Donoghue, 2013), and Dar es Salaam (Kiunsi, 2013). Section 8.5 provides tables of current and indicative future climate risks for Dar es Salaam, Durban, London, and New York.
Many attributes of urban centers can be measured and compared. As noted above, populations vary from a few hundred to more than 20 million. Areas vary from less than one to thousands of square kilometers. Average life expectancy at birth varies from more than 80 years to less than 40 years, and under-five mortality rates vary by a factor of 20 or more (Mitlin and Satterthwaite, 2013). Average per capita incomes vary by a factor of at least 300; so too does the funding available to local governments per person (UCLG, 2010). GHG emissions per person (in tonnes of carbon dioxide equivalent) vary by more than 100 (Dodman, 2009; Hoornweg et al., 2011).
There are large differences between urban centers in the extent to which their economies are dependent on climate-sensitive resources (including commercial agriculture, water, and tourism).There are also large variations in the scale and nature of impacts from extreme weather. As Table 8-2 suggests, there are urban indicators relevant for assessing the resilience to climate change impacts that urban areas have acquired (including the proportion of the population with water piped to their homes, sewers, drains, health care, and emergency
services); it is more of a challenge to find indicators for the climate change related risks and for the quality and capacity of government.
Recent analyses of disaster impacts show that a high proportion of the world’s population most affected by extreme weather events is concentrated in urban centers (UNISDR, 2009, 2011; IFRC, 2010). As shown in Table 8-2, a high proportion of these urban centers lack both local governments with the capacity to reduce disaster risk, and much of the necessary infrastructure. Their low-income households may require particular assistance because of greater exposure to hazards, lower adaptive capacity, more limited access to infrastructure or insurance, and fewer possibilities to relocate to safer accommodation, compared to wealthier residents.
All successful urban centers have had to adapt to environmental conditions and available resources, although local resource constraints have often been overcome by drawing on resources and using sinks from “distant elsewhere” (Rees, 1992; McGranahan, 2007); this includes importing goods that are resource intensive and whose fabrication involves large GHG emissions. The growth of urban population over the last century has also caused a very large anthropogenic transformation of terrestrial biomes. Urban centers cover only a small proportion of the world’s land surface—according to Schneider et al. (2009) only 0.51% of the total land area; only in Western Europe do they cover more than 1%. However, their physical and ecological footprints are much larger. The net ecological impact of urban centers includes the decline in the share of wild and semi-natural areas from about 70% to less than 50% of land area, largely to accommodate crop and pastoral land to support human consumption (Ellis et al., 2010). It has led not only to a decrease in biodiversity but to fragmentation in much of the remaining natural areas and a threat to the ecological services that support both rural and urban areas. Future projections (Seto et al., 2012) suggest that, if current trends continue, urban land cover will increase by 1.2 million km^2 by 2030, nearly tripling global urban land area between 2000 and 2030. This would mean a “considerable loss of habitats in key biodiversity hotspots,” destroying the green infrastructure that is key in helping areas adapt to climate change impacts (Seto et al., 2012, p. 16083) as well as increasing the exposure of population and assets to higher risk levels.
Many of the challenges and opportunities for urban adaptation relate to the central features of city life—the concentration of people, buildings, economic activities, and social and cultural institutions (Romero-Lankao and Dodman, 2011). Agglomeration economies are usually discussed in relation to the advantages for enterprises locating in a particular city. But the concentrations of people, enterprises, and institutions in urban areas also provide potential agglomeration economies in lower unit costs for piped water, sewers, drains, and a range of services (solid waste collection, schools, health care, emergency services, policing) and in the greater capacity for people, communities, and institutions to respond collectively (Hardoy et al., 2001). At the same time, the advantages that come with these concentrations of people and activities are also accompanied by particular challenges—for instance, the management of storm and surface runoff and measures to reduce heat islands. Large cities concentrate demand and the need for ecological services and natural resources (water, food, and biomass), energy, and electricity, and many city enterprises rely on lifeline infrastructure and supply chains that can be disrupted by climate change (UNISDR, 2013; see also Section 8.3.3).
Urban Areas Chapter 8
The increasing concentration of the world’s population in urban centers means greater opportunities for adaptation but more concentrated risk if they are not acted on. Many urban governments lack the capacity to do so, especially those in low- and lower-middle-income nations. The result is large deficiencies in infrastructure and services. Urban centers in high-income nations, although much better served, may also face particular challenges—for instance, aging infrastructure and the need to adapt energy systems, building stock, infrastructure, and services to the altered risk set that climate change will bring (see Zimmerman and Faris (2010) and Solecki (2012) for discussions of this for New York). Many studies have shown that working with a range of government and civil society institutions at local and supra-local levels increases the effectiveness of urban adaptation efforts; support and enabling frameworks from higher levels of government were also found to be helpful (see Section 8.4 and many of the studies listed in Box 8-1).
8.1.4. Vulnerability and Resilience
For each of the direct and indirect impacts of climate change, there are groups of urban dwellers that face higher risks (illness, injury, mortality, damage to or loss of homes and assets, disruption to incomes) (Hardoy and Pandiella, 2009; Mitlin and Satterthwaite, 2013). Age may be a factor (for instance infants and elderly people are more sensitive to particular hazards such as heat stress) or health status (those with particular diseases, injuries, or disabilities may be more sensitive to these impacts). Or it may be that they live in buildings or in locations facing greater risks—for instance on coasts or by rivers with increased flood risks—or that they lack coping capacities. Women may face higher risks in their work and constraints on adaptation if they face discrimination in access to labor markets, resources, finance, services, and influence (see Box CC-GC). These are often termed vulnerable groups— although, to state the obvious, they are vulnerable to direct climate change impacts only to the extent that the hazard actually poses a risk. Remove people’s exposure to the hazard (e.g., provide drains that prevent flooding) and there is limited or no impact. Infants may face serious health risks when water supplies are contaminated by flooding, but rapid and effective treatment for diarrhea and quickly re-establishing availability of drinking quality water greatly reduces impacts (Bartlett, 2008). Adaptations by individuals, households, communities, private enterprises, or government service providers can all reduce risks.
Adaptation in a particular area or settlement may have clear benefits for the inhabitants there, but can also have knock-on effects on the well-being of inhabitants in other areas. Diverting a river course or building an embankment to protect new development may prevent flooding in one location, but may cause or increase flooding somewhere else (see Revi, 2005, for Mumbai; Alam and Rabbani, 2007, for Dhaka).
Assessments of vulnerability to climate change draws on assessments in other contexts—including the vulnerability of low-income groups to stresses and shocks (e.g., Chambers, 1989; Pryer, 2003) and to disasters (Cannon, 1994; Manyena, 2006). The term is generally used in relation to an inability to cope with external changes including avoiding harm when exposed to a hazard. This includes people’s inability to avoid the hazard (exposure), anticipate it, and take measures to avoid it or limit its impact; cope with it; and recover from it (Hardoy and Pandiella,
2009). Vulnerable groups may be identified on the basis of any of these four factors. The definition of resilience used in the WGII AR5 when applied to urban centers means the ability of urban centers (and their populations, enterprises, and governments) and the systems on which they depend to anticipate, reduce, accommodate, or recover from the effects of a hazardous event in a timely and efficient manner (see the Glossary).
The term vulnerability is also applied to sectors, including food processing, tourism, water, energy, and mobility infrastructure and their cross- linkages, for instance, the dependency of perishable commodities on efficient transport. Much tourism is sensitive to climate change, which can damage key tourist assets such as coral reefs and beaches or make particular locations less attractive to tourists because of more extreme weather. The term is also applied to natural systems/ecosystems (e.g., mangroves, coastal wetlands, urban tree canopy). If the adaptive capacity of these systems is increased, they can also provide natural protection from the impacts of climate change in urban areas (see, e.g., Sections 8.2.4.5, 8.3.3.7 for more details).
8.1.4.1. Differentials in Risk and Vulnerability within and between Urban Centers
In urban centers where virtually all buildings meet health and safety standards, where land use planning prevents developments on sites at risk, and where there is universal provision for infrastructure and basic services, the exposure differentials between high- and low-income groups to climate-related risk are quite low. Having low income and few assets in such urban centers does not necessarily imply greater vulnerability to climate change (Mitlin and Satterthwaite, 2013). But typically, the larger the deficit in infrastructure and service provision, the larger the differentials in exposure to most climate change impacts between income groups. Low-income groups in low- and middle-income nations are often disproportionately vulnerable because of poor quality and insecure housing; inadequate infrastructure; and lack of provision for health care, emergency services, and disaster risk reduction (UNISDR, 2009; IFRC, 2010; UN-HABITAT, 2011a; IPCC, 2012; Mitlin and Satterthwaite, 2013). Most deaths from disasters are concentrated in low- and middle-income countries—including more than 95% of deaths from natural disasters between 1970 and 2008 (IPCC, 2012). More than 95% of the deaths from storms and floods registered on the EM-DAT from 2000 to September 2013 were in low- and middle-income nations.^1
An analysis of annual fatalities from tropical cyclones showed these to be heavily concentrated in low-income nations even though there was high exposure in many upper-middle- and high-income nations (and these nations had larger economic losses; UNISDR, 2009). These analyses do not separate rural and urban populations—but there is a growing body of evidence that most urban deaths from extreme weather events are in low-income and lower-middle-income countries (UNISDR, 2009; IFRC, 2010). Analyses of risks across many cities usually show the cities at highest risk from extreme weather or particular kinds of such weather
(^1) These are drawn from data in the The International Disaster Database EM-DAT accessed on September 16, 2013.
Chapter 8 Urban Areas
(e.g., floods) to be primarily in high-income countries (Munich Re, 2004; Hallegatte et al., 2013). But this is because these analyses are based on estimates of economic costs or economic losses. If they were based instead on deaths and injuries, the ranking would change fundamentally (see also Balica et al., 2012). The official statistics on disaster deaths are also known to considerably understate total deaths, in part because many deaths go unrecorded, in part because of the criteria that a disaster event has to meet to be included (one of the following criteria must be fulfilled: ten or more people reported killed; 100 or more people reported affected; declaration of a state of emergency; or call for international assistance) (UNISDR, 2009).
There are dramatic examples of extreme weather events in high-income countries with very large impacts, including high mortality. But the analyses in UNISDR (2009) and IFRC (2010), and the reports of deaths from extreme weather in many of the case studies listed in Box 8-1, suggest that most extreme weather disaster deaths in urban centers are in low- and lower-middle-income nations, and that risks are concentrated in informal settlements. As noted by IPCC (2012), the occupants of these settlements are typically more exposed to climate events with limited or no hazard-reducing infrastructure, low-quality housing, and limited capacity to cope.
Where provision for adequate housing, infrastructure, and services is most lacking, the capacity of individuals, households, and community organizations to anticipate, cope, and recover from the direct and indirect losses and impact of disasters (of which climate-related events are a subset) becomes increasingly important (see Section 8.4). The effectiveness of early warning systems, the speed of response, and the effectiveness of post-disaster response is especially important to those who are more sensitive and have less coping capacity. The effectiveness of such responses depends on an understanding of the specific vulnerabilities, needs, and priorities of different income groups, age groups, and groups that face discrimination, including that faced by women and by particular social or ethnic groups (UN-HABITAT, 2011a).
8.1.4.2. Understanding Resilience for Urban Centers in Relation to Climate Change
In relation to disasters, resilience is usually considered to be the opposite of vulnerability, but vulnerability is often discussed in relation to particular population groups while resilience is more often discussed in relation to the systemic capacity to protect them and reduce the impact of particular hazards through infrastructure or climate-risk sensitive land use management. In recent years, a literature has emerged discussing resilience to climate change for urban centers and what contributes to it (Muller, 2007; Leichenko, 2011; Moench et al., 2011; Pelling, 2011a; Brown et al., 2012; da Silva et al., 2012). Addressing resilience for cities is more than identifying and acting on specific climate change impacts. It looks at the performance of each city’s complex and interconnected infrastructure and institutional systems including interdependence between multiple sectors, levels, and risks in a dynamic physical, economic, institutional, and socio-political environment (Kirshen et al., 2008; Gasper et al., 2011). When resilience is considered for cities, certain systemic characteristics are highlighted—for instance flexibility, redundancy, responsiveness, capacity to learn, and safe failure
(Tyler et al., 2010; Moench et al., 2011; Brown et al., 2012; da Silva et al., 2012), as well as take account of the multiple interdependencies between different sectors (see Section 8.2).
When a specific city is being considered, the level and forms of resilience are often related to specific local factors, services, and institutions—for instance, for each district in a city, will the storm and surface drains cope with the next heavy rainfall? During hot days, will measures to help those at risk from heat stress reach all high-risk groups (see Box CC-HS for more detail)? Here, resilience is not only the ability to recover from the impact but also the ability to avoid or minimize the need to recover and the capacity to withstand unexpected or unpredicted changes (UNISDR, 2011). An important aspect of resilience is the functioning of institutions to make this possible and the necessary knowledge base (da Silva et al., 2012).The emerging literature on the resilience of cities to climate change also highlights the need to focus on resource availabilities and sinks beyond the urban boundaries. It may also require coordinated actions by institutions in other jurisdictions or higher levels of government, for example, watershed management upstream of a city to reduce flood risks (Ramachandraiah, 2011; Brown et al., 2012). There are also the slow onset impacts that pose particular challenges and that may also be outside the jurisdiction of urban governments—for instance, the impact of drought on agriculture, which can raise food prices and reduce rural incomes and demand for urban services.
Resilience to extreme weather for urban dwellers is strongly influenced by factors already mentioned—the quality of buildings, the effectiveness of land use planning, and the quality and coverage of key infrastructure and services. It is also influenced by the effectiveness of early warning systems and public response measures (IFRC, 2010; UN-HABITAT, 2011a) and by the proportion of households with savings and insurance and able to afford safe, healthy homes. Safety nets for those with insufficient incomes are also important, along with the administrative capacity to ensure these reach those in need. Urban governments have importance for most of this, although their capacity to provide usually depends on the revenue raising powers and legislative and financial support from higher levels of government. These in turn are driven in part by political pressure from urban dwellers and innovation by city governments. Private companies or non-profit institutions may provide some of these but the framework for provision and quality control is provided by local government or local offices or national or provincial government.
Cities in high-income nations and many in middle-income nations have become more resilient to extreme weather (and other possible catalysts for disasters) through a range of measures responding to risks and to the political processes that demand such responses (IFRC, 2010; UN- HABITAT, 2011a; Satterthwaite, 2013). The universal provision of piped water, sewers, drains, health care and emergency services, and standards set and enforced on housing quality and infrastructure were not a response to climate change but what was built over the last 100 to 150 years in response to the needs and demands of residents. This has produced what can be termed accumulated resilience in the built environment to extreme weather and built the capacity of local governments to act on risk reduction (e.g., Hardoy and Ruete, 2013, on Rosario, Argentina). In addition, it helped build the institutions, finances, and governance systems that can support climate change adaptation (Satterthwaite, 2013). Building and infrastructure standards can be adjusted as required
Chapter 8 Urban Areas
signals, which may not be well matched with adaptation needs and residual uncertainties. Many are incremental adjustments to current business activities.
For the types of infrastructure most at risk—including most transport, drainage, and electricity transmission systems and many water supply abstraction and treatment works—reserve margins can be increased and back-up capacity developed (WGII AR4 Section 7.6.4). Adaptation of infrastructure and building stock often depends on changes in the institutions and governance framework, for example, in planning regulations and building codes. Climate change has become one of many changes to be understood and planned for by local managers and decision makers (WGII AR4 Section 7.6.7). For instance, planning guidance and risk management by insurers will have roles in locational choice for industry.
Since AR4, a much larger and more diverse literature has accrued on current and potential climate change risks for urban populations and centers (see Section 8.2). The literature on urban “adaptation” and on building resilience at city and regional scales has also expanded (see Sections 8.3, 8.4) including work on urban centers in low- and middle- income nations (see Box 8-1). Far more city governments have published documents on adaptation. There is more engagement with urban adaptation by some professions, including architects, engineers, urban planners, and disaster risk reduction specialists (Engineers Canada, 2008; UNISDR, 2009; Engineering the Future, 2011; UN-HABITAT, 2011a; da Silva, 2012). There are also assessments and books that focus specifically in climate change and cities with a strong focus on adaptation (Bicknell et al., 2009; Rosenzweig et al., 2011; UN-HABITAT, 2011a; Cartwright et al., 2012; Willems et al., 2012; Bulkeley, 2013).
This makes a concise and comprehensive summary more difficult. But it has also allowed for more clarity on what contributes to resilience in urban centers and systems. Specifically, there is now:
- A more detailed understanding of key urban climate processes, including drivers of climate change, and improved analytical and down-scaled integrated assessment models at regional and city scale
- A more detailed understanding on the governance of adaptation in urban centers and the adaptation responses being considered or taken; this includes a large and important gray literature produced by or for city governments and some international agencies and, in many high-income and some middle-income nations, support for this from higher levels of government
- More nuanced understanding of the many ways in which poverty and discrimination exacerbates vulnerability to climate impacts (see also Chapter 13)
- More detailed studies on particular built environment responses to promote adaptation (see, e.g., the growth in the literature on green and white roofs)
- More case studies of community-based adaptation and its potential contributions and limitations
- More consideration of the role of ecosystem services and of green (land) and blue (water) infrastructure in adaptation
- More consideration of the financing, enabling, and supporting of adaptation for households and enterprises
- More on learning from innovation in disaster risk reduction
- A greater appreciation of the interdependencies between different infrastructure networks and of the importance of “hard” infrastructure and of the institutions that plan and manage it
- More examples of city governments and their networks contributing to national and global discussions of climate change adaptation (and mitigation), including establishing voluntary commitments (see, e.g., the Durban Adaptation Charter for local governments) and engaging with the Conference of Parties.
A range of key uncertainties and research priorities emerge from the literature reviewed in this chapter:
- The limits to understanding and predicting impacts of climate change at a fine-grained geographic and sectoral scale
- Inadequate knowledge on the vulnerabilities of urban citizens and enterprises to the direct impacts of climate change, to second- and third-order impacts, and to the interdependence between systems
- Inadequate knowledge on the vulnerability of the built environment, buildings, building components, building materials, and the construction industry to the direct and indirect impacts of climate change and of the most effective responses for new-build and for retrofitting
- Inadequate knowledge on the adaptation potentials for each urban center (and its government) and their costs, and on the limits on what adaptation can achieve (informed by a new literature on loss and damage)
- Serious limitations on geophysical, biological, and socioeconomic data needed for adaptation at all geographic scales, including data on nature-society links and local (fine-scale) contexts (see WMO,
- and hazards
- Uncertainties about trends in societal, economic, and technological change with or without climate change, including the social and political underpinnings of effective adaptation
- Understanding the different impacts and adaptation responses for rapid and slow-onset disasters
- Developing the metrics for measuring and monitoring success in adaptation in each urban center:
- Human deaths and injuries from extreme weather
- Number of permanently or temporarily displaced people and others directly and indirectly affected
- Impacts on properties, measured in terms of numbers of buildings damaged or destroyed
- Impacts on infrastructure, services, and lifelines
- Impacts on ecosystem services
- Impacts on crops and agricultural systems and on disease vectors
- Impacts on psychological well-being and sense of security
- Financial or economic loss (including insurance loss)
- Impacts on individual, household, and community coping capacities and need for external assistance.
8.2. Urbanization Processes,
Climate Change Risks, and Impacts
8.2.1. Introduction
This section assesses the connections between urbanization and climate change in relation to patterns and conditions of climate risk, impact,
Urban Areas Chapter 8
and vulnerability. The focus is on urbanization’s local, regional, and global environmental consequences and the processes that may lead to increased risk exposure, constrain people in high-risk livelihoods and residences, and generate vulnerabilities in critical infrastructure and services. Understanding urbanization and associated risk and vulnerability distributions is critical for an effective response to climate change threats and their impacts (Vale and Campanella, 2005; Bicknell et al., 2009; Solnit, 2009; Bulkeley, 2010; Romero-Lankao and Qin, 2011). It is also critical for the promotion of sustainable urban habitats and the transition to increased urban resilience. There is a particular interest here in the ability of cities to respond to environmental crises, and the resilience and sustainability of cities (Solecki et al., 2011; Solecki, 2012).
The section assesses the direct impacts of climate change on urban populations and urban systems. Together, with shifts in urbanization, these direct impacts change the profile of societal risk and vulnerability. Both can alter transition pathways that lead toward greater resilience and sustainable practices and the basis of how such practices are managed within a community. Understanding and acting on the connections between climate change and urbanization are also crucial because changes in one can affect the other. We investigate a range of direct impacts including those on physical and ecological systems, social and economic systems, and coupled human-natural systems. Where relevant to understanding, cascading impacts (where systems are tightly coupled) and secondary (indirect) impacts also are noted.
8.2.2. Urbanization: Conditions, Processes, and Systems within Cities
8.2.2.1. Magnitude and Connections to Climate Change
The spatial, temporal, and sustainability-related qualities of urbanization are important for understanding the shifting, complex interactions between climate change and urban growth. Given the significant and usually rising levels of urbanization (Section 8.1.3), a growing proportion of the world’s population will be exposed to the direct impacts of climate change in urban areas (de Sherbinin et al., 2007; Revi, 2008; UN-HABITAT, 2011a). Urban centers in Africa, Asia, and Latin America with fewer than a million inhabitants are where most population growth is expected (UN DESA Population Division, 2012), but these smaller centers are “often institutionally weak and unable to promote effective mitigation and adaptation actions” (Romero-Lankao and Dodman, 2011, p. 114).
Urbanization alters local environments via a series of physical phenomena that can result in local environmental stresses. These include urban heat islands (higher temperatures, particularly at night, in comparison to outlying rural locations) and local flooding that can be exacerbated by climate change. It is critical to understand the interplay among the urbanization process, current local environmental change, and accelerating climate change. For example, in the past, long-term trends in surface air temperature in urban centers have been found to be associated with the intensity of urbanization (Kalnay et al., 2006; He et al., 2007; Ren et al., 2007; Stone, 2007; Fujibe, 2008, 2011; Jung, 2008; Rim, 2009; Sajjad et al., 2009; Santos and Leite, 2009; Tayanç et al., 2009; Kolokotroni et al., 2010; Chen et al., 2011; Iqbal and Quamar, 2011). Climate change can influence these microclimate and localized regional
climate dynamics. For example, urbanization (micro scale to meso scale) can strengthen and/or increase the range of the local urban heat island (UHI) altering small-scale processes, such as a land-sea breeze effect, katabatic winds, etc., and modifying synoptic scale meteorology (e.g., changes in the position of high pressure systems in relation to UHI events). Climate modeling exercises indicate an “urban effect” that leads locally to higher temperatures. Building material properties are influential in creating different urban climate temperature regimes, which can alter energy demand for climate control systems in buildings (Jackson et al., 2010).
The dense nature of many large cities has a pronounced influence on anthropogenic heat emissions and surface roughness, linked to the level of wealth, energy consumption, and micro and regional climate conditions. Anthropogenic heat fluxes across large cities can average within a range of approximately 10 to 150 W m –2^ but over small areas of the city can be three to four times these values or even more (Flanner, 2009; Allen et al., 2011). In London, an annual mean anthropogenic heat flux of 10.9 has been observed (Iamarino et al., 2012) with higher values in small areas of the city exceeding 100 (Allen et al., 2011) with a similar range found in Singapore (13 W m –2^ in low-density residential areas and 113 W m–2^ in high density commercial areas (Quah and Roth, 2012). Values locally greater than 1000 W m –2^ have been calculated in Tokyo (Ichinose et al., 1999). Strong seasonal, diurnal, and meteorological variability in temperature also influence the level of significance of urbanization-related changes on specific cities.
The large spatial extent and significant amount of built environment of megacities (10 million or more inhabitants) can have significant impacts on the local and regional energy balance and associated weather, climate, and related environmental qualities such as air quality. Grimmond (2011) found increasing evidence that cities can influence weather (e.g., rainfall, lightning) through complex urban land use-weather-climate directional feedbacks (see also Ohashi and Kida, 2002). Spatially massive urban centers also can affect downwind locations by raising temperature and negatively impacting air quality (Bohnenstengel et al., 2011). Megacity impact on air flows has been modeled for New York and Tokyo (Holt and Pullen, 2007; Thompson et al., 2007; Holt et al., 2009). Megacity-coastal interactions may impact the hydrological cycle and pollutant removal processes through the development of fog, clouds, and precipitation in cities and adjoining coastal areas (Ohashi and Kida, 2002; Shepherd et al., 2002). Other modeling efforts define building density and design and the scale of urban development as important local determinants of the influence of urbanization on local temperature shifts (Trusilova et al., 2008; Oleson, 2012).
8.2.2.2. Spatiality and Temporal Dimensions
Spatial settlement patterns are a critical factor in the interactions among urbanization, climate-related risks, and vulnerability. One aspect is density, ranging from concentrated to dispersed, with most planned urban settlements decreasing in population density with distance from the core (Solecki and Leichenko, 2006; Seto et al., 2012). In cities with large fringe and unplanned settlements, this pattern can be reversed. In both cases, urban growth is experienced through horizontal expansion and sprawl (UN DESA Population Division, 2012), fostering extensive
Urban Areas Chapter 8
Trend period 1901–2012 (°C over period) –0.47 to –0. 0.41 to 0.
0.01 to 0.
–0.4 to –0. –0.2 to 0 0.61 to 0.8 1.51 to 1.
1.251 to 1.
0.81 to 1
1.01 to 1.
1.751 to 2.
0.21 to 0. 0.75–1 million
10 million or more
1–5 million 5–10 million
<1%
5%+
1–3% 3–5%
City population 2010 City population growth rate 1970–
°C
0.75–1 million
10 million or more
1–5 million 5–10 million
City population 2025
(a) Large urban agglomerations 2010 with observed climate change, trend period 1901–
(b) Large urban agglomerations 2025 with projected climate change for the mid-21st century using RCP2.
0.19–0.
2.51–3.
1.51–2. 0.51–1. 1.01–1.
3.01–3. 5.01–5.
4.51–5. 3.51–4. 4.01–4.5 (^) 5.51–6.
2.01–2.
6.01–8.
Continued next pageContinued next page
Figure 8-3 | Large urban agglomerations and temperature change (maps drawn from IPCC, 2013; urban agglomeration population and population growth data from UN DESA Population Division, 2012).
Chapter 8 Urban Areas
growth rate between 1970 and 2010. Those that had the most rapid population growth rates for these 4 decades are strongly clustered in Asia (especially in China and India) and in Latin America and sub- Saharan Africa (with many on the coast). This map highlights the temperature rise of greater than 1°C in areas in north and central Asia, western Africa, South America, and parts of North America, indicating the potential differential exposure of large cities to climate risk.
Figure 8-3b shows the location of the largest urban agglomerations according to projected populations for 2025 within the world map showing projected temperature changes for the mid-21st century, using Representative Concentration Pathway 2.6 (RCP2.6). This is a scenario with strong mitigation. Projected populations for urban agglomerations were not made up to 2050 because there is no reliable basis for making these. Each urban agglomeration’s future population is much influenced by its economic performance and by social, demographic, economic, and political changes that cannot be predicted so far into the future. Assuming that almost all the large urban agglomerations in 2025 will still be large urban agglomerations in 2050, Figure 8-3b suggests that a number of large urban agglomerations in almost all continents, will be exposed to a temperature rise of greater than 1.5°C (over preindustrial levels) by mid-century, using the RCP2.6 scenario (IPCC, 2013).
Figure 8-3c shows a similar map showing projected temperature changes for the mid-21st century but using the RCP8.5 scenario. This
scenario, based on unchanged current GHG emission trends by mid- century, shows that the bulk of the world’s population living in the largest urban agglomerations (based on their 2025 populations) will be exposed to a minimum 2°C temperature rise over preindustrial levels, excluding urban heat island effects. By late-century, under the RCP2. scenario, a number of the urban agglomerations that were among the largest in 2025 will be exposed to temperature rise of up to 2.5°C over preindustrial levels (excluding urban heat island effects), especially in the high latitudes. This implies that mean temperature rise in some cities could be greater than 4°C. The RCP8.5 scenario by late century (with unchanged current GHG emission trends) shows that the bulk of the world’s population living in large urban agglomerations will be exposed to a minimum 2.5°C temperature rise. Some cities in high latitudes experience a mean 3.5°C rise, or greater than 5°C when combined with UHI effects. Peak seasonal temperatures could be even higher. Temperature increases of 6°C to 8°C in the Arctic and temperature rise in Antarctica would contribute to sea level rise that would impact coastal cities across the world.
Increased frequency of hot days and warm spells will exacerbate urban heat island effects, causing heat-related health problems (Hajat et al.,
- and, possibly, increased air pollution (Campbell-Lendrum and Corvalan, 2007; Blake et al., 2011), as well as an increase in energy demand for warm season cooling (Lemonsu et al., 2013). Conversely, widespread reduction in periods of very cold weather will mean a
°C
0.19–0.
2.51–3.
1.51–2. 0.51–1. 1.01–1.
3.01–3. 5.01–5.
4.51–5. 3.51–4. 4.01–4.5 5.51–6.
2.01–2.
0.75–1 million
10 million or more
1–5 million 5–10 million
City population 2025
(c) Large urban agglomerations 2025 with projected climate change for the mid-21st century using RCP8.
6.01–8.
Figure 8-3 (continued)
