Extreme Rain Storms Double in Midwest: Time to Act

NRDC released a report today along with the Rocky Mountain Climate Organization using new analysis that shows rain storms that dump more than three inches in a day have doubled over the last 50 years. Those storms are linked to increased flooding because they’re coming closer together.

When we set out to do this report, we didn’t expect such startling results. But the results are startling: The most severe downpours have doubled over the last century.

In the eight Midwestern states for the worst storms (three inches or more of rain in 24 hours) from 1961-2011:  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).

You can find the full report, press release and individual state data at Doubled Trouble: More Midwestern Extreme Storms.

It documents how the kind of deluges that in recent years washed out Cedar Rapids, IA, forced the Army Corps of Engineers to intentionally blow up levees to save Cairo, IL, and sent the Missouri River over its banks for hundreds of miles are part of a growing trend.

One example, in Milwaukee in 2010 7.9 inches of rain fell in a 24 hour period. The city averages 32 inches per year. Here's a very startling video of what this much rain looked like:


“This study's results highlight real issues that have already caused significant pain and suffering in Milwaukee,” said Kevin Shafer, executive director, Milwaukee Metropolitan Sewerage District. “We have learned that we can no longer sit on our hands and hope that extreme rainfall events are not going to happen.  We need to explore new ways to soften the impacts of these events and to better protect our residents.  In Milwaukee, we are adding green infrastructure to our landscape, reinforcing our grey infrastructure, converting to renewable energy for all our wastewater facilities, and educating our public about what they can do be better prepared for flooding.  In these tight economic times, it is not a popular message, but, having lived through it, we understand that it is better than the alternatives.”

Doubled Trouble: More Midwestern Extreme Storms adds several years of data to previous reports tracking the issue of Midwestern storms.  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.

Karen Hobbs of our Midwest office, a former senior Chicago water official, noted of the report:

“It 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. 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 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. (you can find what kind of extreme has been happening where you live by punching in your zip code here, and learn about this cool new tool here.)

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.

Our long-time collaborator and primary report author Stephen Saunders, the president of the Rocky Mountain Climate Organization said of the report: 

“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.”

That’s why we need to keep working with state and local governments to ensure that green infrastructure techniques are fully incorporated into infrastructure capital planning projects. 

Green infrastructure captures rain where it falls, preventing it from flooding storm drains, overwhelming sewer systems, and polluting water sources. To accomplish this, green infrastructure techniques include planted swales around parking lots, rain gardens, rain barrels and cisterns, green roofs, permeable pavement and trees to help soak up or capture water. You can read more about these types of solutions in NRDC's Rooftops to Rivers report.

Rooftops to Rivers features case studies for 14 geographically diverse cities that are all leaders in employing green infrastructure solutions to address stormwater challenges. These generally cheaper and quicker actions provide beneficial uses for stormwater, cut water pollution, save money, and beautify cityscapes. The cities we feature recognized that stormwater, once viewed as a costly nuisance, can be transformed into a community resource. They’ve found green infrastructure is a more cost effective approach than investing in "gray," or conventional, infrastructure, such as underground storage systems and pipes. At the same time, each dollar of investment in green infrastructure delivers other benefits that conventional infrastructure cannot, including more flood resilience and, where needed, augmented local water supply.