IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability Vulnerable urban populations

Urbanisation and climate change may work synergistically to increase disease burdens. Urban populations are growing faster in low-income than in high-income countries. The urban population increased from 220 million in 1900 to 732 million in 1950, and is estimated to have reached 3.2 billion in 2005 (UN, 2006b). In 2005, 74% of the population in more-developed regions was urban, compared with 43% in less-developed regions. Approximately 4.9 billion people are projected to be urban dwellers in 2030, about 60% of the global population, including 81% of the population in more-developed regions and 56% of the population in less-developed regions.

Urbanisation can positively influence population health; for example, by making it easier to provide safe water and improved sanitation. However, rapid and unplanned urbanisation is often associated with adverse health outcomes. Urban slums and squatter settlements are often located in areas subject to landslides, floods and other natural hazards. Lack of water and sanitation in these settlements are not only problems in themselves, but also increase the difficulty of controlling disease reservoirs and vectors, facilitating the emergence and re-emergence of water-borne and other diseases (Obiri-Danso et al., 2001; Akhtar, 2002; Hay et al., 2005a). Combined with declining economies, unplanned urbanisation may affect the burden and control of malaria, with the disease burden increasing among urban dwellers (Keiser et al., 2004). Currently, approximately 200 million people in Africa (24.6% of the total population) live in urban settings where they are at risk of malaria. In India, unplanned urbanisation has contributed to the spread of Plasmodium vivax malaria (Akhtar et al., 2002) and dengue (Shah et al., 2004). In addition, noise, overcrowding and other possible features of unplanned urbanisation may increase the prevalence of mental disorders, such as depression, anxiety, chronic stress, schizophrenia and suicide (WHO, 2001). Problems associated with rapid and unplanned urbanisation are expected to increase over the next few decades, especially in low-income countries.

Populations in high-density urban areas with poor housing will be at increased risk with increases in the frequency and intensity of heatwaves, partly due to the interaction between increasing temperatures and urban heat-island effects (Wilby, 2003). Adaptation will require diverse strategies which could include physical modification to the built environment and improved housing and building standards (Koppe et al., 2004).