Human Health and Climate Change
179
and the Caribbean in 2002 they killed almost 20 times as many people as malaria and dengue fever combined (Warren and others 2006). Extreme weather events, such as floods and heavy rains, increase the incidence of waterborne diseases, but other important causes are the risky water storage and water use practices of people who lack access to clean water and sanitation. Accordingly, the risk of waterborne diseases is expected to increase as a result of climate change and variability—an expectation that is supported by the evidence of El Niño’s influence on diarrheal diseases. Evidence is ample of the link between extreme weather events and waterborne diseases is ample. Following Hurricane Mitch, the number of cholera cases was four times higher than normal in Guatemala and six times higher in Nicaragua (IPCC 2001b). On the Pacific Coast of South America, outbreaks of cholera have been tied to extreme weather caused by El Niño; about 11,700 people died from cholera in Peru between 1991 and 1996. Similarly, when temperatures were higher than normal during El Niño in 1997–98, an unusually large number of people suffering from diarrhea and dehydration were admitted to hospitals for rehydration treatment in Lima. Indeed, a time-series analysis showed an 8 percent increase in admissions due to diarrhea for each 1°C increase in temperature (WHO 2003). In tropical climates diarrheal diseases normally peak during the rainy season, and studies from the United States have shown that about half of all waterborne diseases can be attributed to extreme rainfall (WHO 2003). Most of the waterborne microorganisms that cause disease derive from human or animal feces, which heavy rains and flooding can transport into groundwater as well as surface and well water. Sources of drinking water can thus become contaminated with E. coli bacteria and other microorganisms. Communities that have combined systems for storm water drainage and sewage run the risk of accidental releases of raw sewage. Heavy rainfall can lead to surface runoff that allows pathogens to enter aquifers, wells, and drinking water. Because one of the projected aspects of climate change is more frequent heavy rains, such contamination is likely to escalate, causing a surge in the incidence of waterborne diseases. However, underlining the complexity of forecasting the health impact of climate change, the seasonal pattern of cholera outbreaks in the Amazon basin has been associated with lower river flow in the dry season (Gerolomo and Penna 1999). Rising temperatures may lengthen the season, or alter the geographical distribution, of waterborne diseases, inasmuch as most of the protozoa, viruses, and bacteria that cause them thrive in warm water and weather.