William Petroski: Iowa faces more big rainstorms, big floods; in 2001-2010 there were 52% more storms per year

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Cedar Rapids residents affected by flooding in 2008. / Register FIle Photo

Iowa faces more big rainstorms, big floods

by William Petroski, Des Moines Register, May 16, 2012

Big storms, leading to big floods, are occurring with greater frequency in the Midwest with the incidence of severe flooding doubling in the last half-century, according to a report issued today by two environmental groups.

The study by the Natural Resources Defense Council and the Rocky Mountain Climate Organization says the kind of deluges that led to flooding in 2008 in Cedar Rapids and caused Missouri River flooding last year in western Iowa are part of a growing climate trend.

Between 1961 and 2011, Iowa had a 32% increase in storms that brought three or more inches of rain, said the report, titled, “Doubled Trouble: More Midwestern Extreme Storms.”

“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,” said Stephen Saunders, the president of the Rocky Mountain Climate Organization and the report’s lead author.

Saunders said a threshold may have already been crossed so that major floods in the Midwest should no longer be considered purely natural disasters, but instead mixed natural/unnatural disasters. And if emissions continue to increase, the forecast is for more extreme storms in the region, he added.

The report’s key findings include:

* Since 1961, the Midwest has had more large storms. The largest of storms, those of 3 inches or more of precipitation in a single day, increased by 103% over the roughly half century period through 2011. For storms of at least 2 inches but less than 3 inches in a day, the trend was a 81% increase; for storms of 1-2 inches, a 34% 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% 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 7 of the 9 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 . By 2001-2010, the average return period for Midwestern extreme storms at a single location was to 2.2 years—or 4-8 times more frequent than major hurricanes.

The analysis said the two worst years in the Midwest for storms of 3 inches or more per day were 2008 and 1993, which had the Midwest’s worst floods in about 80 years, causing $16 billion and $33 billion in damages, respectively, and ranking among the nation’s worst natural disasters. In 2010, which ranked 4th among years in regional extreme-storm frequency, Iowa alone had $1 billion in agricultural losses, the study said. In 2011, which ranked 5th, Midwestern flooding caused $2 billion in damages. This shows how the Midwest is increasingly vulnerable to flooding if extreme precipitation continues with human caused-climate change, the study concluded.

“This report confirms what most of us in the Midwest have known for a while; violent storms are becoming more frequent. And the nation’s crumbling water infrastructure just makes the problem worse,” said Karen Hobbs, a senior policy analyst for the National Resources Defense Council. “Most of our communities were not designed to handle the volume of water dumped by these epic storms. But green infrastructure solutions, such as green roofs, street trees and rain gardens, literally capture rain where it falls, helping prevent flooding and providing communities with greater resiliency to these ferocious storms.”

The report suggests the federal government should lead the way in protecting the Midwest from even more severe storms in the future. The recommendations include enacting mandatory requirements to reduce emissions by at least 20% by 2020 and by 80% by 2050; protecting the Clean Air Act Authority of the U.S. Environmental Protection Agency; overcoming barriers to investment in energy efficiency; and working with state and local governments to ensure that green infrastructure techniques are incorporated into construction projects.


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