Research via the Rocky Mountain Climate Organization
Devastating extreme rain events are part of a growing trend in the Midwest, according to a new report looking at 50 years of storm data.
Over the last five decades, the types of deluges that washed out towns in Iowa, forced the Army Corps of Engineers to intentionally blow up levees to save Cairo, Illinois, and sent the Missouri River over its banks for hundreds of miles, have been increasing, according to analysis 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’s lead author, Stephen Saunders, explained that “a threshold may have been crossed”:
“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.
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).
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.
The report also presents new evidence linking extreme storms in the Midwest to major floods, the region’s most costly regularly occurring 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 percent of the local precipitation came from extreme storms.
In 2010, which ranked fourth among years in regional extreme-storm frequency, Iowa alone had $1 billion in agricultural losses from extreme storms. In 2011, which ranked fifth, Midwestern flooding caused $2 billion in damages. This shows how the Midwest is increasingly vulnerable to flooding if extreme precipitation continues to increase with human-caused climate change, as scientists consistently project will happen.
This research brief was originally published at the Rocky Mountain Climate Institute.