Climate change to increase chances of flooding, disease, researchers say
Extreme rainfall events in southern Wisconsin will become 10 to 40 percent stronger as the climate continues to change toward the end of the century, resulting in greater potential for flooding and waterborne diseases that often accompany high sewage diversion into Lake Michigan, University of Wisconsin researchers predict.
Moreover, the frequency of heavy rainfalls -- those with at least 2.5 inches of daily rain -- is expected to rise by 50 percent to 120 percent in Chicago, according to researchers who used computer modeling to make their predictions.
That means that the heavy rainfalls that have occurred in the Chicago area once every other year recently will happen an average of 1.2 times per year by the end of the 21st century, the study said.
"Increased heavy runoff events put our drinking and recreational water at risk of contamination," said Jonathan Patz, a professor at the University of Wisconsin School of Medicine and Public Health who co-authored the report.
"We used several global climate models and brought them down to the region so we get a realistic forecast for the future," Patz said. "And we have health and contamination data from Wisconsin and Chicago."
The moisture-holding capacity of the atmosphere increases with temperature, the study noted.
The researchers say that a trend toward extreme weather such as the monsoon-like rainfalls in parts of the Great Lakes region this year is likely to aggravate the risk for outbreaks of waterborne disease for the 40 million people who depend on the lakes for drinking water.
The main threat to human health comes when heavy rain overwhelms the urban stormwater and sewage systems of Milwaukee and Chicago, resulting in millions of gallons of raw sewage being diverted to Lake Michigan, Patz said.
Waterborne diseases caused by bacteria, viruses and parasites are among the most common health risk of drinking water. In 1993, Milwaukee experienced an outbreak in city drinking water of the parasite Cryptosporidium that exposed more than 400,000 people and killed more than 50.
Adding to the risk are concentrated livestock operations where heavy rainfall can wash large amounts of animal waste into the rivers and streams that drain into the Great Lakes.
"It's the perfect storm," said Patz. "Deteriorating urban water infrastructure, intensified livestock operations, and extreme climate change-related weather events may well put water quality, and thereby our health, at risk."
A previous study by Patz showed that two-thirds of waterborne disease outbreaks between 1948 and 1994 were correlated with heavy rainfall.
Better surveillance of fecal pollution is needed, instead of detecting contamination after an outbreak, the researchers said. Patz and fellow UW-Madison researcher Stephen Vavrus also said that sewage and stormwater systems should be upgraded and that better land use planning could reduce runoff of nutrients, toxic chemicals and micro-organisms.
The study is published in the Oct. 7 American Journal of Preventive Medicine.
Patz, who is also affiliated with the UW-Madison's Nelson Institute for Environmental Studies, conducted the study with Vavrus, a climatologist and director of the Nelson Institute's Center for Climatic Research; Christopher Uejio of the Nelson Institute; and Sandra McLellan of the UW-Milwaukee. Funding came from the U.S. Environmental Protection Agency and the National Oceanic and Atmospheric Administration.
