Study of US Midwest finds increase in heavy rainfalls over 60 years

Iowa Now at the University of Iowa: Heavy rains have become more frequent in the upper Midwest over the past 60 years, according to a study from the University of Iowa. The trend appears to hold true even with the current drought plaguing the region, the study's main author says.

The fact that temperatures over the country's midsection are rising, too, may be more than coincidence.The hotter the surface temperature, which has been the trend in the Midwest and the rest of the world, the more water that can be absorbed by the atmosphere. And the more water available for precipitation means a greater chance for heavy rains, explains Gabriele Villarini, assistant professor in engineering at the UI and lead author of the paper, published in the Journal of Climate, the official publication of the American Meteorological Society.

“We found that there is a tendency toward increasing trends in heavy rainfall in the northern part of the study region, roughly the upper Mississippi River basin,” says Villarini, in the civil and environmental engineering department and an assistant research engineer at the IIHR-Hydroscience and Engineering. “We tried to explain these results in light of changes in temperature. We found that the northern part of the study region—including Minnesota, Wisconsin, Iowa, and Illinois—is also the area experiencing large increasing trends in temperature, resulting in an increase in atmospheric water vapor.“

Villarini notes the current drought affecting the Midwest and other regions of the country has occurred too recently to be included in his study, whose data goes from about 1950 to 2010.

“I’m not looking at the average annual rainfall. I’m studying heavy rainfall events,” he says. “We may currently be in deficit for overall rainfall, but we may also be in the normal range when it comes to the number of heavy rainfall days.”...

Crows in a puddle, shot by torbakhopper, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license