CHICAGO, Ill. — Johnson County, Ind., still has scars from the flood that ravaged its towns and rural areas in 2008.

The lake dam that gave way under the surge of water to make national news was replaced last fall, and the water is slowly inching its way back up the banks. Some homeowners who lost their homes only recently received checks for disaster assistance from the government, following years of heartache and uncertainty.

Such deluges of rain have also forced the U.S. Army Corps of Engineers to intentionally blow up a levee to save Cairo, Ill., and swelled the Missouri River over its banks for hundreds of miles.

Huge rainfalls and flooding in the Midwest are part of a growing trend, according to a new report by the Rocky Mountain Climate Organization (RMCO) and the Natural Resources Defense Council (NRDC). Severe downpours have doubled over the last 50 years, the report stated.

“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,” said Stephen Saunders, president of the RMCO and the report’s lead author.

The report, Double Trouble: More Midwestern Extreme Storms, focused on Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio and Wisconsin. Key findings included:

•Since 1961, the Midwest has had an increasing number of large storms. The largest of storms – those of 3 inches or more of precipitation in a single day – increased the most, with their annual frequency having gone up by 103 percent over the roughly half-century through 2011. For storms of at least 2 inches but fewer than 3 inches in a day, the trend was an 81 percent increase; for storms of 1-2 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, 2001-10, showing the greatest jumps.

For the largest storms in 2001-10, 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 1961-70, extreme storms averaged once every 3.8 years at an individual location in the Midwest.

By 2001-10, the average return period for Midwestern extreme storms at a single location was down to 2.2 years.

The report also shows the two worst years in the Midwest for storms of 3 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, respectively, and rank among the nation’s worst natural disasters.

In 2010, which ranked fourth among years in regional extreme-storm frequency, Iowa alone had $1 billion in agricultural losses from them. In 2011, which ranked fifth, Midwest 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, according to the report, as scientists consistently project will happen.