A critical need for sector-specific analyses of climate hazards and vulnerabilities, and location-specific adaptive capacities and mitigation strategies, has been highlighted in the most recent IPCC Working Group III AR4 (IPCC, 2007c), and the World Resource Institute (Baumert et al, 2005; Bradley et al, 2007), and OECD (Hunt and Watkiss, 2007; Hallegatte et al, 2008). Several examples in the literature exist which highlight these omissions and deficiencies. For example, most analyses on climate impact assessments and cities have neglected non-coastal cities, and uncertainties in assessing the economic impacts need to be incorporated, particularly for developing-country cities where variances are likely to be higher (Hunt and Watkiss, 2007, and Hallegatte et al., 2008). Overall, there is a pressing call for understanding risks associated with climate change as they pertain to different types of cities – coastal versus non-coastal and developed versus developing; different sectors – physical infrastructure such as energy, transport, water supply, as well as social services such as health and environmental management (and the complex interactions among these sectors); and differential impacts on the poor or the young and old, who are more vulnerable than the rest of the urban population.
Furthermore, city-specific efforts should graduate from awareness raising to impact assessments – including costing impacts and identifying co-benefits-and-costs – and adaptation analysis so that "no-regret adaptation options" can be adopted to increase resilience of cities to climate change. Economic costs of climate change in cities should "bracket" for uncertainty and assess both intra- and inter-sectoral and systemic risks to address direct and indirect economic impacts.
Understanding how cities craft institutional mechanisms to respond to climate change is another important element of the urban risk assessment process. This has been briefly explored, where relevant, for detailed case studies on Quito and Durban (see Carmin and Roberts, 2009) and the eight-stage Risk, Uncertainty and Decision-Making Framework developed by the UK Climate Impacts Programme (2009), which aims "to help decision-makers identify and manage their climate risks in the face of uncertainty."
Figure 2.1: Urban climate change vulnerability and risk assessment framework.
To further explore current practices and potential of urban climate risk assessment, we define and examine the characteristics and interplay of three basic risk elements in framework format: hazards, vulnerability, and adaptive capacity (see Figure 2.1).The challenge in the research community is to translate information on each and from climate science into knowledge that triggers a realistic assessment of the vulnerability of the city and its systems so as to facilitate the development of pragmatic adaptation strategies. In the remainder of this topic we detail this challenge through the articulation of four city-level case studies around the three following objectives:
1. Characterize the hazards associated with climate change at the city-level;
2. Identify the most vulnerable segments (people, locations, sectors) of the city, and
3. Assess the city’s ability to adapt to anticipated changes in climate.
Hazards are defined in the framework as the climate-induced stresses and climate-related extremes and are identified through observed trends and projections derived from global climate models (GCMs) and regional downscaling (see Table 2.1). Extreme events affected by climate change include heat waves, droughts, inland floods, accelerated sea level rise, and floods for coastal cities. The variables examined to track these climate-related hazards are temperature, precipitation, and sea level (see Figures 2.2-2.22). In essence, the hazard element presents an array of climate change information and insights into the key stresses that potentially have the greatest consequence for any specific city. In this regard, it is critical to draw attention to both the variation in climate means and the change in frequency and intensity of extreme events. The latter offers opportunities for linkages with disaster risk reduction programs and has received perhaps more attention, while the former has critical long-term implications for city infrastructure and development, and tends to receive less attention because the mean changes are gradual.
Analysis of hazards specific to a particular city should include observed and projected data on key climate parameters -temperature, precipitation, sea level rise, among others. Further, each hazard needs to be analyzed for variance in climate parameters over the short and long term and, where relevant, for frequency as well as intensity of extreme events. Climate change scenarios provide a reasonable understanding of potential future climate conditions (Parsons et al., 2007). It is not expected that a single climate model will project exactly what will happen in the future, but by using a range of climate model simulations along with scenarios incorporating different atmospheric concentrations of greenhouse gases, a range of possible climate outcomes are produced and can be presented as projections that demonstrate the current expert knowledge.
Local climate change information for cities can be derived from the scenarios of greenhouse gas emissions and global climate model simulations described above. For the case-study cities that are examined below, quantitative projections are made for key climate variables such as the change in mean temperature that reflect a model-based range of values for the city-specific model grid boxes (see Table 2.5). Further, there is a need for a nuanced understanding of the complex interactions between hazards and the city. This is because the city can be both a producer as well as a receiver of these hazards. For instance, New York City alone contributes about 0.25 percent of global greenhouse gas emissions (The City of New York, 2007). On the other hand, increase in sea level also increases the city’s susceptibility to flooding. In addition, while both urban heat island and global warming increase the ambient temperature of the city, one is internally generated while the other is externally induced.
Vulnerability is defined as the physical attributes of the city and its socio-economic composition that determine the degree of its susceptibility. The variables affecting vulnerability include flood proneness (proximity to coast or river), land area, elevation, population density, percentage of poor, and quality of infrastructure. The OECD’s work on city vulnerability in the context of climate change points to such variables as location, economy, and size as well (Hunt and Watkiss, 2007). More detailed indicators such as composition of the poor population – age, gender, labor force composition, and the like – need to be taken into consideration when in-depth city vulnerability analysis is conducted. For our evaluation here a more restricted set of variables that is readily available for most cities was utilized. These variables illustrate that such physical and socio-economic characteristics affect a city’s risk.
Vulnerability is defined as the extent to which a city is predisposed to "adverse effects of climate change, including climate variability and extremes" (IPCC, 2007d). However, unlike the IPCC definition of vulnerability that includes adaptive capacity, we decouple the two here and address them individually, considering vulnerability to be determined by the physical and underlying social conditions of the city while adaptive capacity is determined predominantly by the change agents. In turn, vulnerability is a function of a host of city characteristics, including but not limited to the location of a city, particularly its proximity to a salt water coastline or other large water body, topography or any other physical attributes of the landscape or physical geography that make the city susceptible to climate variations.
Social factors that determine the degree of vulnerability of a city include its population size and composition, density, size of city, quality of infrastructure, type and quality of its built environment and its regulation, land use, governance structure and the like. A critical factor determining the vulnerability of the poor as opposed to the non-poor population of the city is the percentage of the population living in slums. These are households that lack access to one or more of the following: improved water supply, improved sanitation, sufficient living space, structurally sound dwellings, and security of tenure (UN-HABITAT, 2003). The contrast between the formally planned part of the city and the slums is stark and is a key determinant of the differential vulnerability of the poor as opposed to the non-poor (UN-HABITAT, 2008a).
Adaptive capacity includes institutional attributes of the city and its actors that determine the degree of its capability to respond to potential climate change impacts. Thus they provide measures of the ability (institutional structure, caliber, resources, information, analysis), and willingness of actors (local governments, their constituent departments, private sector, civil society, NGOs, academics) to adapt to climate change. Variables that can determine the extent of a city’s ability to adapt include the structure and capacity of institutions, presence of adaptation and mitigation programs, and motivation of change agents. Here it is critical to draw a distinction with the term "resilience" that the IPCC (2001b) Working Group II assessment defined as "amount of change a system can undergo without changing state." In contrast, adaptive capacity does not assume a steady state of a city and its integrated systems; rather it measures the ability and willingness to not only cope but to respond positively to the stresses that climate change imposes.
Adaptive capacity is the ability and willingness of the city’s key stakeholders to cope with the adverse impacts of climate change and depends on the awareness, capacity, and willingness of the change agents. A quick measure of institutional awareness is the presence of a comprehensive analysis of climate risks for the city and corresponding adaptation and mitigation initiatives. Capacity here refers to the quality of institutions at various levels of governments – local, regional, and national – and within local government, across various departments. Further, the capacity of the private sector, non-governmental organizations, and community groups to respond also matters. Finally, the willingness to act is of the essence. In this regard, identifying in substantial detail the leading actors for climate response – government, private sector, and civil society – and mapping their initiatives is essential in estimating adaptive capacity of a city.