From: Editor, NRDC
Published May 22, 2012 08:40 AM

Climate Study: Extreme Rain Storms in Midwest Have Doubled in Last 50 Years, Often Leading to Worsened Flooding

The kind of deluges that in recent years washed out Cedar Rapids, IA, forced the Army Corps of Engineers to intentionally blow up levees to save Cairo, IL, and sent the Missouri River over its banks for hundreds of miles are part of a growing trend, according to a new report released today by the Rocky Mountain Climate Organization (RMCO) and the Natural Resources Defense Council (NRDC). Big storms, leading to big floods, are occurring with increasing frequency in the Midwest, with incidences of the most severe downpours doubling over the last half century, the report finds.

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Stephen Saunders, the president of the Rocky Mountain Climate Organization and the report's lead author, said: "Global studies already show that human-caused climate change is driving more extreme precipitation, and now we've documented how great the increase has been in the Midwest and linked the extreme storms to flooding in the region. A threshold may already have been crossed, so that major floods in the Midwest perhaps now should no longer be considered purely natural disasters but instead mixed natural/unnatural disasters. And if emissions keep going up, the forecast is for more extreme storms in the region."

In addition to region-wide trends, the report presents trends in the eight Midwestern states. For the worst storms (three inches or more of rain in 24 hours) from 1961-2011, the report outlines the following state-level trends: Indiana (+160 percent); Wisconsin (+203 percent); Missouri (+81 percent); Michigan (+180 percent); Minnesota (+104 percent); Illinois (+83 percent); Ohio (+40 percent); and Iowa (+32 percent).

Titled, "Doubled Trouble: More Midwestern Extreme Storms," the new NRDC-RMCO report adds several years of data to previous reports tracking the issue of Midwestern storms. Key findings include:

- Since 1961, the Midwest has had an increasing number of large storms. The largest of storms, those of three inches or more of precipitation in a single day, increased the most, with their annual frequency having increased by 103 percent over the roughly half century period through 2011. For storms of at least two inches but less than three inches in a day, the trend was a 81 percent increase; for storms of one to two inches, a 34 percent increase. Smaller storms did not have a significant increase.

- The rates of increase for all large storms accelerated over time, with the last analyzed decade, 2001-2010, showing the greatest jumps. For the largest storms, in 2001-2010 there were 52 percent more storms per year than in the baseline period.

- The frequency of extreme storms has increased so much in recent years that the first 12 years of this century included seven of the nine top years (since 1961) for the most extreme storms in the Midwest.

- With more frequent extreme storms, the average return period between two such storms has become shorter. In 1961-1970, extreme storms averaged once every 3.8 years at an individual location in the Midwest. That is two to four times more frequent than a major hurricane making landfall at a typical location along the U.S. coast from North Carolina to Texas. By 2001-2010, the average return period for Midwestern extreme storms at a single location was down to 2.2 years—or four to eight times more frequent than landfalling major hurricanes.

Article continues at NRDC

Flood image via Shutterstock

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