Current climate extremes and projections for future changes to climate have resulted in growing attention to the health effects of climate on all human populations, urban and rural (McMichael et al., 2003; Confalonieri et al., 2007; Costello et al., 2009). Indeed, almost all the impacts of climate change have direct or indirect consequences for human health. However, for a number of reasons, city dwellers – especially those in low- and middle-income nations – are especially vulnerable to the health impacts of climate change.
In this topic we present issues and case studies relevant to human health in cities under climate change conditions. In Section 7.2, we discuss the most relevant conclusions from the health topic of the IPCC Fourth Assessment Report (Confalonieri et al., 2007), looking at its application to cities. In Section 7.3, we present an overview of urban health outcomes and their climate-related drivers. In Section 7.4 the factors that can modify the impacts of climate change on human health in urban areas are discussed. Section 7.5 presents examples and case studies of adaptations that protect city residents from some of the health impacts and risks posed by climate change. A brief discussion of needed changes in energy, transportation, and other sectors to reduce emissions of harmful pollutants and provide co-benefits for human health is found in Section 7.6. The urgent need for better, more urban focused and targeted research is discussed in Section 7.7. Conclusions are presented in Section 7.8.
Why health and climate change for cities?
Urban populations are increasing in absolute numbers and relative to rural populations in every part of the world. According to the United Nations Population Fund (2007) the world is undergoing the largest wave of urban growth in history. In 1800 there were only 2 cities larger than a million inhabitants. By 1950 there were 75 cities of this size and by 2000 there were 380 "million-cities," half of these in Asia (Satterthwaite et al., 2008). Cities have also grown larger. In 2000, the largest 100 cities had an average of 6.3 million inhabitants. In 2008, more than half of the world’s population was living in cities and their surrounding areas. By 2030 this number is projected to reach almost 5 billion, with urban growth concentrated in Africa and Asia. While meg-acities are important a great deal of the new growth will occur in smaller towns and cities, which tend to have fewer resources (Bicknell and Dodman, 2009).
Because cities concentrate populations, extreme weather events such as intense precipitation, cyclonic storms, or storm surges affect a much larger number of people than when they strike less populated regions. Such damages may be exacerbated in the future, since extreme weather events are expected to increase in number and intensity under climate change (IPCC, 2007). Cities also concentrate poor populations who are especially vulnerable to the effects of climate change because of the conditions in which they live. In low- and middle-income countries, poor slum dwellers can make up 50 to 60 percent of the urban population, living in precarious structures, often with little access to water, sanitation, electricity, health care, or emergency services (Huq et al., 2007).
The concentration of populations in urban areas also tends to lengthen the supply lines for essentials such as water, food, and energy sources, and makes them more dependent on waste collection (and more susceptible when waste is not collected). Storms, floods, or droughts that disrupt these urban lifelines can have serious consequences for the health of city dwellers (McBean and Henstra, 2003).
Many cities are located in areas that are vulnerable to both existing and projected climate hazards. Most of the world’s mega-cities were originally established on seacoasts or beside major rivers that enabled trade and commerce or territorial control (Huq et al., 2007). Cities such as Venice (Italy) and Mumbai (India), located on low-elevation seacoasts, are particularly vulnerable to sea level rise and storm surges. Of 180 countries with populations in low-elevation coastal zones, about 70 percent have large urban areas extending into that zone (McGranahan et al., 2007). As cities have grown, many have expanded from their original, secure locations onto river deltas and floodplains, marshlands, or up steep hillsides and into other areas that are poorly suited for human habitation and are vulnerable to weather extremes. In many cases the expansion of the city itself has created hazards by filling in water courses or cutting down adjacent forests, increasing the risk of floods and landslides.
The ways in which cities are constructed – reducing vegetation, covering large areas with impermeable surfaces, and obstructing natural drainage channels – make many city dwellers more vulnerable to heat waves, heavy precipitation, and other extreme weather events, which are already increasing, likely as a result of climate change.
Many cities, even in high-income countries, are exposed to multiple stresses not related to climate change. Such stresses include lack of financial resources to meet the needs and demands of a growing population; aging, poorly maintained, inadequate, or non-existent infrastructure; poor land use planning and enforcement; inadequate resources for disaster preparedness; self-serving political institutions or outright corruption that divert resources from pressing problems; and increasing income disparity and growing numbers of impoverished families living in unplanned, unserviced settlements and slums (Satterthwaite et al., 2008). Severe weather events can combine with some or all of these stresses to create conditions of extreme hazard as demonstrated recently by:
• flash floods and landslides in Caracas, which killed 30,000 people in 1999 (Satterthwaite et al., 2008)
• floods in Shanghai in 1998, which killed 3,000 and displaced 16 million in the Yangtze basin (de Sherbinin et al., 2007)
• extreme heat in Paris in the summer of 2003, which contributed to an estimated 2,085 deaths out of a total of 15,000 for the whole of France (le Tertre et al., 2006)
• monsoon floods in 2005 in Mumbai, which killed more than 1,000 (de Sherbinin et al., 2007)
• intense rainfall combined with high-tide conditions that submerged more than 100 square kilometers of Dhaka in 1988, 1998, and 2004 (Alam and Rabbani, 2007)
• hurricane Katrina, which devastated New Orleans in 2005 and killed more than 1,800 people (Glantz, 2008).
In each of these instances, more than 1,000 people died and many more suffered serious health effects. Unless more action is taken to address the risk factors from current extreme weather events and from future climate change, events of this kind are very likely to become more common, and their health impacts will be even more severe.
Ways in which climate change will affect the health of city dwellers
Climate change is expected to exacerbate a number of existing threats to human health and well-being rather than to introduce new health effects (Costello et al., 2009). Both direct and indirect impacts on human health are beginning to be observed under current climate conditions and are predicted to be amplified in the coming decades. The health of city dwellers is expected to be affected in the following ways:
• direct physical injuries and deaths from: extreme weather events such as tropical cyclones and other major storms with high winds; storm surges; intense rainfall that leads to flooding; or ice storms that damage trees and overhead structures and produce dangerous transport conditions
• illnesses resulting from the aftermath of extreme weather events that destroy housing, disrupt access to clean water and food and increase exposure to biological and chemical contaminants
• water-borne diseases following extended or intense periods of rainfall, ground saturation and floods and saline intrusion due to sea level rise
• food-borne diseases resulting from bacterial growth in foods exposed to higher temperatures
• illnesses and deaths from the expanded range of vector-borne infectious diseases
• respiratory illnesses due to worsening air quality related to changes in temperature and precipitation resulting in the formation of smog
• morbidity and mortality, especially among the elderly, small children, and people whose health is already compromised, as a result of stress from hotter and longer heat waves – which are aggravated by the urban heat island effect
• malnutrition and starvation among the urban (and rural) poor who have reduced access to food as a result of drought-induced shortages and price rises
• uprooting and migration of populations negatively affected by climate events to areas that are unable to provide the services they need.
The challenge for cities
As a primary climate change prevention measure, cities need to contribute more effectively to reducing their greenhouse gas emissions (Frumkin et al., 2008).While emission reductions will not prevent many of the damaging climate changes that are already underway and likely to continue in the next 50 to 100 years, it remains a critical task for high-income cities and countries, and for some middle-income cities and countries whose emissions are rapidly growing. Emission reductions will moderate the expected impacts of climate change over the long term. However, as Huq et al. (2007) and Sat-terthwaite et al. (2008) argue, low-income cities and their most vulnerable residents contribute relatively little to the worldwide complement of greenhouse gas emissions and thus the focus of their efforts will likely be more on identifying vulnerabilities and preparing adaptation strategies.
Because the world has failed so far to prevent the build-up of greenhouse gases in the atmosphere and thus to prevent health impacts that climate change is likely to inflict on city dwellers, a key task is to alter existing urban conditions that may combine with climate change and result in deaths, injuries, and illnesses in the population. In low- and middle-income cities and countries this requires a focus on meeting basic development needs -adequate housing; provision of infrastructure that supplies clean water, sanitation, and energy; education; and primary health-care services. Provision of these services will reduce vulnerability to many of the health impacts of climate change and increase the capacity of the most vulnerable to withstand some of the impacts that cannot be avoided. High-income cities already provide these services to most of their population, but often do this in a way that interacts with weather extremes to worsen impacts – by paving much of the urban landscape, for example, which exacerbates heat and flooding. Whether building new structures and services or modifying existing ones, cities need to alter the urban characteristics that worsen the impacts of extreme weather events and turn at least some of them into health and economic disasters. Anticipated climate change over the lifetime of the structures should also be taken into account. Otherwise such investments may be jeopardized by climate change.
In addition to long-term vulnerability reduction, cities need to undertake disaster preparedness planning, and develop early warning and emergency disaster relief systems (Few et al., 2006). This will necessitate identifying, assessing, and monitoring disaster risks. The World Bank (2008) Climate Resilient Cities primer recommends preparing a disaster history and a city hazard profile map to identify areas vulnerable to natural hazards, an essential task for disaster planning. In addition to helping with longer-term adaptation planning, these actions will aid in the development of shorter-term plans to avoid disasters in areas that have proved to be prone to recurrent calamities. Improved urban planning and linking it to disaster risk reduction in climate change adaptation strategies will be necessary (Revi, 2008; GFDRR, 2009). Recovery and reconstruction will benefit from preparatory measures.
All these tasks are a challenge, though they are easier for higher-income cities, which are reasonably well-organized and resourced. A great many cities have committed to reducing emissions – and some have very ambitious targets. A smaller number of cities and urban regional governments have developed and are in the early stages of implementing plans to adapt to climate change (Penney, 2007; Bicknell and Dodman, 2009). The Cities of Stockholm and Toronto and the Greater London Authority have explicitly incorporated health concerns in their plans and activities (Ekelund, 2007; Toronto Environment Office, 2008; Mayor of London, 2008).
Cities in low-income countries face a much larger hurdle to prepare for climate change, for they need to develop basic structures and services to support adequate housing, water, sanitation, energy distribution, transportation, education, and health-care services and at the same time consider how to do this in a way that will increase adaptation and resilience for their residents and citizens. Some researchers express skepticism about the likelihood that municipal governments will act "to protect the populations within their jurisdiction from risks arising from climate change when they have shown so little inclination or ability to protect them from other environmental hazards" (Satterthwaite et al., 2008, p. 2). They emphasize the need for support from national governments to provide the legal and institutional basis for reducing the risks from climate change and for support from the international community to provide the financial resources. They also discuss successful examples of engaging communities at risk in the process of determining how to adapt and, in some cases, where to move risky settlements (Huq et al., 2007).
