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Doubled Trouble
More Midwestern Extreme Storms

Changes in frequencies of storms in the Midwest, by category of storm size for five decades, 1961-1970 through 2001-2010.
Labeled changes are for the last decade. Comparisons are to frequencies in 1961-1990.

The Rocky Mountain Climate Organization and Natural Resources Defense Council have released a new report, Doubled Trouble: More Midwestern Extreme Storms, which starkly documents how much heavy precipitation has increased in the Midwest and sheds new light on the devastating and costly floods that have hammered the region, especially in recent years.

New RMCO analysis of a half century of precipitation data across the Midwest, defined as Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, and Wisconsin, indicates the region has had an increasing number of large storms since 1961. The largest of storms—those of three inches or more of precipitation in a single day—have increased the most, with their annual frequency more than doubling over the past 51 years. The frequencies of all large storms, especially the largest, have particularly spiked this century.

Notable results of the study include:

  • The annual frequency of three-inches-plus storms increased by 103% from 1961 through 2011, while for storms of at least two inches but less than three inches in a day, the trend was an 81% increase; for storms of one to two inches, a 34% increase; and for smaller storms of less than one inch, a statistically insignificant 8% increase.
  • 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.
  • A different way to present the same data is in the graphic at the top of this page, which shows the average number of storms per decade, compared to a 1961-1990 baseline.
  • The average return period between two extreme storms at a single location in the Midwest has shrunk from once every 3.8 years in 1961-1970, to once every 2.2 years in the last decade. That recent rate is four to eight times more frequent than landfalling major hurricanes at a typical location along the U.S. coast from Texas to North Carolina.

   The report also presents new evidence linking extreme storms in the Midwest to major floods, the region's most costly regularly ocurring natural disasters. The new analysis shows that the two worst years in the Midwest for storms of three inches or more per day were 2008 and 1993, the years with the Midwest's worst floods in some 80 years, which caused $16 billion and $33 billion in damages and rank among the nation's worst natural disasters. The report presents new evidence linking the 2008 flooding to extreme storms, showing that, in areas with the worst flooding, 48% of the local precipitation came from extreme storms.

As Stephen Saunders, president of RMCO and the report's primary 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.”

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The report has received robust media attention. National and even international news media coverage included articles by major wire services, including Reuters and McClatchy, with coverage by many major newspapers in the region, including the Chicago Tribune, Indianapolis Star, Detroit News, Des Moines Register, St. Paul Pioneer Press, and Dayton Daily News, as well as many local publications and websites. Extensive TV and radio coverage included CBS St. Louis, St. Louis Public Radio, WXOW (local TV), and Minnesota Public Radio.
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