Study: Extreme Rain Storms In Midwest Have Doubled In Last 50 Years

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.

6 Responses to Study: Extreme Rain Storms In Midwest Have Doubled In Last 50 Years

  1. The graph is inadequately labeled. What does each bar represent? I’m guessing it’s decades, but it’s not clear and needs fixing. And what is the percentage relative to? The mean over the past 50 years, or the preceding period?

  2. Nealo says:

    Here’s what you need to make sense of the graph (from the RMCO link):
    “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.”

  3. David F. says:

    Not too surprised by the conclusions of this study. My hometown (in the American midwest) has seen two 100-year floods within the past decade, and five of the ten wettest years since the late 19th century have occurred since 2000.

    What is more surprising is that some continue to deny these trends! I was browsing through a book on weather that was originally published around 2000. There was only a few pages devoted to climate change, but even then (more than ten years ago), there was a recognition that extreme weather events were on the increase. And this trend has only become more marked in recent years.

    Of particular note, that book highlighted that weather disaster related insurance claims during the 1980s were more than tenfold claims during the 1960s, and that they were even higher in the 90s. In fact, the damage losses during 1998 (aided by the Super El Nino) exceeded losses for the entire decade of the 1980s.

    Of course, we know now that insurance claims related to weather disasters have continued to increase dramatically during the 2000s. I don’t know how this trend could possibly be explained merely by a slight population growth, the theory favored by confusionists such as RP, Jr.

  4. David F. says:

    Given how rapidly some of the changes are occurring in recent years, I’m actually surprised more so-called skeptics aren’t jumping ship. Here, in the United States, for instance, in the past twelve months, we’ve had the 2nd warmest summer on record (behind only the Dust Bowl summer of 1936, the 4th warmest winter (the three warmer winters have all occurred in the past 20 years), and are in the midst of what will almost assuredly be the warmest spring on record (March was warmest, April 3rd warmest, and May has continued the trend of anomalous warmth). We are also currently in the midst of the warmest 12-month period on record, and the warmest year-to-date period.

    Despite all of this, it seems the denialists have simply redoubled their efforts to cast doubt on the science. It would seem that belief that climate change isn’t occurring or isn’t caused by the observed increase in greenhouse gases is an irrational belief, yet these denialists have cast belief in climate change as irrational (as evidenced by the Heartland Institute ad campaign).

  5. Merrelyn Emery says:

    Storms of My Grandchildren – coming early, ME

  6. Mulga Mumblebrain says:

    Climate scientists have just discovered that the last fifty years in Australia were the hottest in one thousand years. However I know with absolute certainty that the denialist industry, led by the Murdoch media, will assail these findings with pseudo-science, innuendo, disinformation and flat paranoid accusations of conspiracy and fraud. It is as dependable as the sunrise.