8.4.2.4 Populations in coastal and low-lying areas

One-quarter of the world’s population resides within 100 km distance and 100 m elevation of the coastline, with increases likely over the coming decades (Small and Nicholls, 2003). Climate change could affect coastal areas through an accelerated rise in sea level; a further rise in sea-surface temperatures; an intensification of tropical cyclones; changes in wave and storm surge characteristics; altered precipitation/runoff; and ocean acidification (see Chapter 6). These changes could affect human health through coastal flooding and damaged coastal infrastructure; saltwater intrusion into coastal freshwater resources; damage to coastal ecosystems, coral reefs and coastal fisheries; population displacement; changes in the range and prevalence of climate-sensitive health outcomes; amongst others. Although some Small Island States and other low-lying areas are at particular risk, there are few projections of the health impact of climate variability and change. Climate-sensitive health outcomes of concern in Small Island States include malaria, dengue, diarrhoeal diseases, heat stress, skin diseases, acute respiratory infections and asthma (WHO, 2004a).

A model of a 4°C increase of the summer temperature maximum in the Netherlands in 2100, in combination with water column stratification, projected a doubling of the growth rates of selected species of potentially harmful phytoplankton in the North Sea, increasing the frequency and intensity of algal blooms that can negatively affect human health (Peperzak, 2005). Projections of impacts are complex because of substantial differences in the sensitivity to increasing ocean temperatures of phytoplankton harmful to human health.

The population at risk of flooding by storm surges throughout the 21st century has been projected based on a range of global mean sea-level rise and socio-economic scenarios (Nicholls, 2004). Under the baseline conditions, it was estimated that in 1990 about 200 million people lived beneath the 1-in-1,000-year storm surge height (e.g., people in the hazard zone), and about 10 million people/yr experienced flooding. Across all time slices, population growth increased the number of people living in a hazard zone under the four SRES scenarios (A1FI, A2, B1 and B2). Assuming that defences are upgraded against existing risks as countries become wealthier, but sea level rise is ignored, the number of people affected by flooding decreases by the 2080s under the A1FI, B1 and B2 scenarios. Under the A2 scenario, a two-to-three-fold increase is projected in the number of people flooded per year in the 2080s compared with 1990. Island regions are especially vulnerable, particularly in the A1FI world, especially in South-East Asia, South Asia, the Indian Ocean coast of Africa, the Atlantic coast of Africa and the southern Mediterranean (Nicholls, 2004).

Densely populated regions in low-lying areas are vulnerable to climate change. In Bangladesh, it is projected that 4.8% of people living in unprotected dryland areas could face inundation by a water depth of 30 to 90 cm based on assumptions of a 2°C temperature increase, a 30 cm increase in sea level, an 18% increase in monsoon precipitation, and a 5% increase in monsoon discharge into major rivers (BCAS/RA/Approtech, 1994). This could increase to 57% of people based on assumptions of a 4°C temperature increase, a 100 cm increase in sea level, a 33% increase in monsoon precipitation, and a 10% increase in monsoon discharge into major rivers. Some areas could face higher levels of inundation (90 to 180 cm).

Studies in industrialised countries indicate that densely populated urban areas are at risk from sea-level rise (see Chapter 6). As demonstrated by Hurricane Katrina, areas of New Orleans (USA) and its vicinity are 1.5 to 3 m below sea level (Burkett et al., 2003). Considering the rate of subsidence and using the TAR mid-range estimate of 480 mm sea-level rise by 2100, it is projected that this region could be 2.5 to 4.0 m or more below mean sea level by 2100, and that a storm surge from a Category 3 hurricane (estimated at 3 to 4 m without waves) could be 6 to 7 m above areas that were heavily populated in 2004 (Manuel, 2006).