Extreme rainfall events have caused major flooding issues in Minnesota, Wisconsin and Iowa this year, and it's part of a growing trend in the Upper Midwest.
According to FiveThirtyEight, heavy rain events have been increasing over the last 100 years in Minnesota, including the number of "mega-rain" events, which are defined as storms that produce six inches of rain over at least 1,000 square miles – and at least eight inches of rain are recorded in the center of coverage area.
According to the Minnesota Department of Natural Resources, Minnesota has documented 11 mega-rain events since 1973. It notes:
"Of these 11 events, two were in the 1970s, one was in the 1980s, none were in the 1990s, but four occurred in both the 2000s, and the 2010s (still underway). Thus, the 18 years from 2000-2017 have seen nearly three times as many mega-rains as the 27 years spanning 1973-99."
Ironically, FiveThirtyEight's story was published on May 17, about a month before northeast Minnesota and northwest Wisconsin were hammered with 5-15 inches of rain that caused extreme flash flooding in area rivers, creeks and streams.
The non-stop rain over the weekend of June 16-17 caused the Nemadji River south of Superior to rise 25 feet in just two days. Countless roads in the area were closed due to water covering roadways or completely washing sections of roads away.
MPR meteorologist Paul Huttner said that the 15 inches of rain that fell in Drummond, Wisconsin were about two inches more than needed to qualify as a 1 in 1,000-year rain event.
Then, this past weekend, extreme rainfall plagued northern Iowa, with a football field in Forest City showing the power of heavy rain when it started to bubble up, taking on a jello-like composition after eight inches of rain fell in about an hour.
Not only are prolific rains becoming more common, they're changing the way engineers are planning for the future. Read the full FiveThirtyEight article for more on that.
The DNR notes that climatologists believe the increase in mega-rain events is due to global warming, which provides storms with more moisture to work with.