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Report Shows Increase In Rainfall, Floods For Mississippi Basin 

A recently released report by a senior National Weather Service (NWS) meteorologist shows in more detail the increase in rainfall and flood events in the Mississippi River basin in recent years.

The report, titled “Precipitation Trends in the Mississippi River Watershed,” was prepared by Bill Frederick, who serves as the National Weather Service liaison at the Corps of Engineers’ Mississippi Valley Division. It builds on earlier reports, including the 2014 National Climate Assessment, which noted, “Heavy downpours are increasing nationally, especially over the last three to five decades … this increase has been greatest in the Northeast, Midwest and Upper Plains—more than 30 percent above the 1901–1960 average. There has also been an increase in flooding events in the Midwest and Northeast, where the largest increases in heavy rain amounts have occurred.”

The new report concludes that there has been a 37 percent increase in very heavy rain events over the Midwest during the past few decades, increasing the frequency and magnitude of flood events.

One table of the new report compares flood events during various 30-year periods at Cairo, Ill. “While the first seven 30-year periods ranged from 13-20 percent occurrences, the last three 30-year periods have risen to about double that, with 30-38 percent of the years from 1972 to 2017 exceeding the NWS major flood stage of 53 feet at Cairo,” according to the report. While the likelihood of minor and moderate flood events has remained within a narrow range, “the greatest percentage difference has occurred in the major flood stage category.”

The report notes that an “interesting trend” occurs at the confluence of the Arkansas and Mississippi rivers. “Although there is a corresponding increase in precipitation and very heavy rain events as at Cairo, flood occurrences have diminished dramatically since the 1940s. This corresponds with the river cut-off program that began in the 1940s, which was completed in the 1960s along the Mississippi River from Memphis, Tenn., to near Natchez, Miss.”

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