Extreme rain events could be new norm in Illinois

The expression “when it rains, it pours” certainly sums up the weather pattern much of this growing season in Illinois.

Those who received steady rounds of rain absorbed massive downpours that caused extensive flooding, particularly in parts of northern, southwest and southeast Illinois in recent weeks.

Meanwhile, there are farmers in portions of Illinois, and more so in states west of the Mississippi River, who probably still feel like they can’t buy a rain this season.

So, what’s with the extreme disparity in rainfall events? Convective thunderstorms typically generate a wide range of rainfall within a small geographical area, and that’s just what the jet stream is funneling right through the state as the subtropical flow from the south and northern polar jet merge.

“We’re in a region where we’re seeing the two jet streams come together,” meteorologist Jim Rasor said at the Illinois Wheat Association’s summer forum in Okawville (Washington County). “The jet streams are like the train tracks and the storms are the trains.”

And some of the storms that barreled into Illinois on this track dropped close to a foot of rain or more in some areas in recent weeks. Some of the heavy downpours were fed by nearly unbearable humidity, at times.

“We’re already wetter than normal down here [in southern Illinois] for the month because of one rain event,” Rasor said.

The stretch of extreme rainfall events improved topsoil moisture ratings in the state to 18% surplus, 58% adequate and 24% short or very short as of Aug. 8. Almost one-third of topsoil moisture ranked short or very short back on July 11.

But there are still areas of the state quite short on moisture. Portions of Champaign County and the southern tips of Alexander and Pulaski were in severe drought as of Aug. 11, according to the U.S. Drought Monitor. Moderate drought also remains an issue in all or parts of DeWitt, Douglas, Edgar, Piatt and Vermilion counties in east central Illinois and in Hancock, Henderson, McDonough and Warren counties to the west.

The weather outlook favors hotter and drier conditions to the north and warm, muggy and wet conditions to the south the next 45 days, with a fairly mild and dry forecast for harvest, Rasor said.

Long term, the rise in rainfall disparity and extreme precipitation events could persist.

“Climate change is real,” Rasor said. “A warmer atmosphere will hold more humidity and more humidity will make more rain. But we’re also getting extended dry periods in the summer [in between storms].”

Since 1981, the frequency of daily 2-plus-inch rain events has doubled, Eric Snodgrass, principal atmospheric scientist at Nutrien Ag Solutions, previously told FarmWeek.

“The frequency of 500-year flood events is increasing,” he said.

But that’s not the case everywhere, as evidenced by the multi-year drought in the southwest and western U.S.

“For us, we’re getting the rain,” Rasor said. “But other places are getting less.”

In fact, changing precipitation patterns are causing a shift in the Corn Belt, said Elwynn Taylor, Iowa State University climatologist.

“We’ve been getting increasing moisture in the Corn Belt, including almost all of Illinois. It’s pushing the Corn Belt to the north and west,” Taylor previously told FarmWeek.

The geographical center of the Corn Belt was located over Springfield in 1950, but has since moved to Peoria by 1964, the Quad Cities in the next decade and currently sits close to Des Moines, Iowa, Taylor said.

“Minnesota was barely part of the Corn Belt [in the mid-1900s] and now is a major part of it [along with the Dakotas],” he said. “The reason is precipitation.”

• Daniel Grant writes Farm Week. This story was distributed through a cooperative project between Illinois Farm Bureau and the Illinois Press Association. For more food and farming news, visit FarmWeekNow.com.