In 2012, the Natural Resources Defense Council (NRDC) released a study on how "Extreme Rain Storms in Midwest Have Doubled in Last 50 Years, Often Leading to Worsened Flooding."  Some major media outlets – such as Reuters and the Christian Science Monitor – covered the NRDC study with the following quotes:

Twice as many mega rainstorms in Midwest in past 50 years: Wisconsin saw the biggest rise (203 percent) in extreme rainstorms – 3 inches of rain or more in a day, new study says. Climate change is behind more Midwest flooding, say scientists ...

The number of extreme rainstorms – deluges that dump 3 inches or more in a day – doubled in the U.S. Midwest over the last half-century, causing billions of dollars in flood damage in a trend climate advocates link to a rise in greenhouse gas emissions ...

Extreme rains became floods that washed out the city of Cedar Rapids, Iowa, in 2008; forced the U.S. Army Corps of Engineers to blow up Mississippi River levees to save Cairo, Illinois, in 2011; and, also in that year, sent the Missouri River over its banks for hundreds of miles.

About that flood in Cedar Rapids, Iowa during 2008.  Here are annual peak flows at the USGS hydrometric station for the Cedar River at Cedar Rapids back to 1903 (there is a single datapoint for 1851, but continuous yearly records don't begin until the 1900s).

The 2008 flood was certainly historically unprecedented, well above the previous record.  But it was not part of a significant trend.  There have been no significant trends in the annual peak flow since records began, or since 1970, or during the last three decades.  Consequently, assigning this flood event to climate change – and specifically, anthropogenic climate change – seems impossible.

The Mississippi River's peak flow in 2011 near Cairo, Illinois wasn't close to a record event.  At the nearest hydrometric station – the Mississippi River at Thebes, IL just 20 miles upstream – the 2011 peak flow was 876,000 cubic feet per second (cfs), well below the record peak flow of 1,075,000 cfs set on July 4, 1844, and ranked only fifth highest behind 1844, 1993, 1943, and 1973.  There are no signs of significant trends in the river's peak flows since records began, or since 1970, or during the past 30 years.  Actually, the last three decades has seen a correlation toward lower peak flows, not higher.  Seems impossible to chalk this event up to anthropogenic climate change as well.

Notable towns affected by that 2011 flood on the Missouri River included Bismarck, ND; Omaha, NE; Sioux City, IA; and Kansas City, MO.  Here are the annual peak flow series for the Missouri River at Bismarck, the Missouri River at Omaha, Nebraska; the Missouri River at Sioux City, IA; and the Missouri River at Kansas City, MO since their respective records began in the USGS database.

Click to enlarge.

There appears to be no chance the 2011 floods were caused by anthropogenic climate change. The peaks flows in 2011 were neither historically anomalous nor part of significant trends toward increasing peak flows.

Finally, there is this quote from the NRDC report's press release:

Stephen Saunders, the president of the Rocky Mountain Climate Organization and the report's lead 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.'

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) ...

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 ... 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.

Of the 43 climate sub-regions across these 8 states, only five sub-regions have significant increasing trends in the number of days per year having three inches or more of precipitation over the last 50 years.  Just two of the eight states (Ohio and Michigan) have significant increasing trends when the sub-regions within each state are summed, and over the past three decades both these states move to having massively non-significant trends.  It appears that the number of large storms each year is not increasing throughout the vast majority of the Midwest, and the frequency certainly does not appear to be accelerating.

The NRDC report promoted climate alarmism, but a re-evaluation of the claims made therein and their association to climate change is likely in order.