Heavy rainfall and flooding have long been known to increase the risk of waterborne infectious diseases by exposing people to contaminated floodwaters and overwhelming water and sanitation systems. In a study published today in the American Journal of Epidemiology, researchers at Berkeley found that, without accurate measurement of climate variables like rainfall, we may be substantially underestimating the impact of extreme weather on the global incidence of diarrheal diseases.
Diarrhea remains among the leading causes of child mortality. During periods of heavy rainfall and floods, pathogens can disperse with floodwaters, causing disease in locations far from their original sources. According to study lead Morgan Levy, a postdoctoral fellow and environmental scientist at the UC Berkeley School of Public Health, the complex configuration of rainfall measurements, flooding, and exposed populations that are typical of epidemiologic studies can obscure the connection between climate and waterborne diseases.
“We found that the greater distance between measurements of extreme rainfall and vulnerable populations, the more we underestimate the impact of extreme events on health,” she says.
In collaboration with earth scientists and epidemiologists, Levy combined simulation studies with analysis of health and environmental data from research in northern coastal Ecuador. The research team found that when rainfall is measured far from a vulnerable population, the estimated effect of extreme rainfall on diarrheal disease incidence is underestimated by as much as 45 percent.
“Our results demonstrate how important it is to accurately assess exposure to extreme weather events,” says Levy, “particularly in countries where environmental information is limited, and where the frequency and intensity of extreme weather are expected to change with a changing climate.”
As the global climate changes, populations are vulnerable to a range of new conditions—from more frequent heat waves to more intense hurricanes—that will impact health. According to Associate Professor Justin Remais, chair of the Environmental Health Sciences division at the School of Public Health, a deeper understanding of the health effects of these changes will require greater collaboration between epidemiologists and earth scientists. “By committing to improved characterization of environmental processes in epidemiologic research,” says Remais, “we stand the best chance of understanding and responding to the health effects of extreme climate, and can take the most appropriate actions to protect populations from these exposures.”
The research team included scientists from the University of Michigan, University of Colorado, Emory University and University of Nevada Reno. The study was supported by grants from the National Institute of Allergy and Infectious Diseases, the National Science Foundation, and the National Institute of Health’s Fogarty International Center.
By Austin Price