Midwest flooding more frequent

http://www.eurekalert.org/pub_releases/2015-02/uoi-sfm020915.php

Public Release: 9-Feb-2015 Study finds Midwest flooding more frequent
Research covered more than 50 years of data in 14 states
University of Iowa

The U.S. Midwest and surrounding states have endured increasingly more frequent flood episodes over the past half-century, according to a study from the University of Iowa.

The UI researchers based their findings on daily records collected by the U.S. Geological Survey at 774 stream gauges in 14 states from 1962-2011, a data-collection period in common for all the stations.

They found that 264 (34 percent) of the stations had an increase in frequency in the number of flood events, while only 66 stations (nine percent) showed a decrease.

"It's not that big floods are getting bigger, but that we have been experiencing a larger number of big floods," says Gabriele Villarini, UI assistant professor of civil and environmental engineering and corresponding author on the paper, published Feb. 9 in the advance online edition of the journal Nature Climate Change.

The findings likely come as no surprise to millions of people in the Midwest and bordering states. During the past several decades, large floods have plagued the region in 1993, 2008, 2011, 2013 and again in 2014. The floods have caused agricultural and economic losses in the billions of dollars, displaced people and led to loss of life.

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He notes that seasonal analysis revealed that most of the flood peaks in the upper Midwest occur in the spring and stem primarily from snow melt, rain falling on frozen ground and rain-on-snow events. Interestingly, spring--in addition to being a season with increasing frequency of heavy rainfall--also has the strongest increase in temperature over most of the northern part of the region studied, he says.

The findings jibe well with current thinking among climate scientists about how the hydrological cycle is being affected by global warming. In general, as the atmosphere becomes warmer, it can hold more moisture. One consequence of higher water vapor concentrations is more frequent, intense precipitation.

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