Impacts Of Climate Change On Cities

Given their concentration of people, industry, and infrastructure, cities and built environments are generally expected to face significant impacts from climate change. Some of the most important impacts will be associated with changes in the frequency and intensity of extreme weather. Hurricane Katrina in 2005 illustrated the potential for extreme events to cause catastrophic damage to human well-being as well as urban infrastructure; likewise, temperature extremes in cities increasingly cause severe human and environmental impacts, even in the developed world (see Box 12.1). The impacts of warming are amplified in large urban conglomerations because of the heat island effect and the interaction of other environmental stressors (Grimmond, 2007; Hayhoe et al., 2004; Rosenzweig et al., 2005; Solecki et al., 2005). For example, the urban heat island of Phoenix raises the minimum nighttime temperature in parts of the city by as much as 12.6°F (7°C), generating serious water, energy, and health consequences (Brazel et al., 2000). The growth of the southwestern U.S. "sunbelt" as well as that of megacities throughout other arid regions of the world increases the populations at risk from extreme heat as well as their demand for energy and water (Rosenzweig et al., 2005).

In addition, CO2, nitrogen oxides, volatile organic compounds, particulate matter, and other pollutants and pollutant precursors react in the urban airshed to produce high levels of surface ozone and other potential health hazards (see Chapter 11). In a warmer future world, stagnant air, coupled with higher temperatures and absolute humidity, will lead to worse air quality even if air pollution emissions remain the same (e.g., Cifuentes et al., 2001 a,b In many cases, air pollution plumes extend well beyond the urban area per se, affecting people and agriculture over large areas, such as the Ganges Valley (e.g., Auffhammer et al., 2006). In the developing world, such decreases in outdoor air quality come on top of poor indoor air quality—for example, from wood fuel heating (Zhang and Smith, 2003).

As discussed in Chapter 11, certain groups (such as the elderly) are especially vulnerable to intensive heat waves in cities worldwide, especially in temperate climates. Groups with preexisting medical problems, without air-conditioned living quarters, who are socially isolated, or who live on top floors are particularly vulnerable (Naugh-ton et al., 2002; Patz et al., 2005; Semenza et al., 1996). The elderly, as well as portions of the population with asthma and related problems, are also susceptible to poor air quality (e.g., Hiltermann et al., 1998). The U.S. population over age 65 is expected to reach 50 million (20 percent of the total U.S. population) by 2030, with the overwhelming majority living in cities. Cities throughout the nation and the world are differentially prepared (CCSP, 2008a), as illustrated by the relative success of Marseille in the

BOX 12.1

Urban-Climate Interactions and Extreme Events

In the summer of 2003, a persistent anticyclone anchored above western Europe triggered temperatures in excess of 95°F-99°F (35°C-37°C) for as long as 9 days (see figure below). Temperatures were especially high in cities, where urban heat islands amplified the maximum temperatures (Beniston, 2004) and ground-level ozone concentrations climbed to 130 to 200 |ig/m3 (equivalent to the Environmental Protection Agency's code orange alert; Pirard et al., 2005). It is estimated that this heat wave and the associated poor air quality caused more than 50,000 excess deaths, mostly among elderly urbanites (Bruker, 2005). In France alone, where the housing infrastructure from Paris to Marseille commonly does not include air conditioning or insulation between roofs and rooms, more than 14,800 excess deaths occurred during that period, and the number of deaths is positively correlated with the number of consecutive hot days (Pirard et al., 2005). The rash of deaths, including over 2,200 excess deaths on a single day in August, overwhelmed emergency rooms and morgues.

The 2003 summer heat wave in Europe. Colors indicate differences in daytime surface temperature between July 2003 and July 2001. Dark red areas across much of France indicate that temperatures in 2003 were as much as 10°C (18°F) higher than in 2001. SOURCE: Earth Observatory, NASA {http://earthobservatory.nasa. gov/NaturalHazards/view.php?id= 11972).

The 2003 summer heat wave in Europe. Colors indicate differences in daytime surface temperature between July 2003 and July 2001. Dark red areas across much of France indicate that temperatures in 2003 were as much as 10°C (18°F) higher than in 2001. SOURCE: Earth Observatory, NASA {http://earthobservatory.nasa. gov/NaturalHazards/view.php?id= 11972).

2003 heat wave over France (Box 12.1; Pirard et al., 2005) versus the 700 excess deaths in Chicago's 1995 heat wave (Semenza et al., 1996). As noted in Chapter 11 and consistent with the findings of the panel report Adapting to the Impacts of Climate Change (NRC, 2010a), research on health infrastructure and preparedness, especially in urban complexes, is needed to inform practice.

Other climate change impacts will also affect cities. Many of the 635 million people occupying coastal lands worldwide live less than 33 feet (10 meters) above sea level and are thus threatened by sea level rise (McGranahan et al., 2007; Wu et al., 2002, 2009; see Chapter 7). Existing tensions over water withdrawal between rapidly growing urban areas and agricultural sectors will be exacerbated by decreasing snowpack in the American West and other regions as a result of climate change and variability (NRC, 2007b). Water vulnerabilities in general are expected to pose major problems for cities in the developing world (Vorosmarty et al., 2000). Expected increases in the frequency of extreme events (Milly et al., 2002), such as intense and prolonged rain storms (see Chapter 8) that stress drainage and flood protection systems, also threaten aging urban infrastructure. Climate change impacts on the megalopolises will also stress regional ecosystem function, water withdrawal, and movement of biota, among other environmental issues (Folke et al., 1997; Grimm et al., 2008; IHDP, 2005).

Cities are centers of economic, cultural, educational, research, social, and political activity, and as such they experience a myriad of nonclimatic changes and stresses that affect their institutional, technological, and economic capacities, the social capital available within and among different population groups, and the relationships between urban centers and their surroundings. Climate change impacts cannot be fully appreciated and addressed without understanding the complex nature of multiple stressors and interacting climatic and nonclimatic factors that affect the vulnerability and adaptive capacity of cities (e.g., Campbell-Lendrum and Corvalan, 2007; Pelling, 2003).

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