Lower risk of spring flooding in northern Illinois this year

SOMONAUK, Ill. — The potential for flooding in northern Illinois during the spring is much lower as compared to the last two years.

“The top and subsoil moisture is below to near average, so there is a lot of capacity to take in precipitation in the winter and spring,” said Trent Ford, Illinois state climatologist based at the Illinois State Water Survey, part of the Prairie Research Institute at the University of Illinois.

“We have come off three wet years, and we had a dry fall,” said Mark Tuttle, who farms with his two sons near Somonauk. “We’ve had some snowfall and the rivers are down, so I’m concerned about the subsoil moisture, but there’s plenty of time for that to happen.”

Farmers prefer a drier planting season to get the crop in the ground and established.

“I think we’re looking for a great year, if we can get the crop in the ground on time,” said the president of DeKalb County Farm Bureau. “I’m very optimistic for the ag economy because prices are up, so we have a chance to forward contract and lock in some profit.”

Tuttle plants corn, soybeans and wheat and has a small cow herd.

“We’re up to 80 acres of wheat this year, which is the most we’ve ever grown,” he said. “Wheat works for us for erosion as a great cover crop in the winter, and when we have spring rains, we’ve got something on our hills.”

Typically, Tuttle divides his acres into 40% corn, 40% soybeans and 20% wheat.

“If we have a late spring, we might plant more beans,” he said. “I planted corn on June 2 two years ago — and I’m not going to do that again.”

Tuttle will plant corn up until Memorial Day.

“After that, we’re going to do something else,” he said. “This year, I will plant my 41st crop.”

Rain, Rain And More Rain

Precipitation from April 2019 to March 2020 in northern Illinois was the wettest on record, said Ford during a presentation at CropFlix, the 2021 Crop Management Conference. “We came into March 2020 with soils at or near saturation, streams were at bank full or above and overall there was a pretty significant risk of flooding.”

For both 2019 and 2020, the first three months of the year were wetter than average.

“From April 1 to May 31, we began to see some differences,” Ford said. “The only area that was nearly as wet in 2020 as it was in 2019 was the Chicagoland area, and the rest of the area was 3 to 6 inches drier, which made a large difference in the extent of the flooding issues and planting delays.”

There was also a difference in how frequently the precipitation fell between the two years.

“In 2019, from April 1 to May 31, Chicago’s O’Hare Airport reported 20 days with a least one-quarter of an inch of rain, so there was not a whole lot of time between rains events to let the fields dry down and get fieldwork done,” Ford said. “In 2020, the rain was less than half that, so there were periods where conditions were dry enough and temperatures were warm enough for planting.”

Snow pack was also quite different in 2019 and 2020.

“Because February and March were so warm in 2020, we had very small snow pack in Wisconsin and Minnesota and almost no snow pack in Iowa or Illinois, so that helped reduce flooding in the spring,” Ford said.

It was very cool in April and May of 2020 with temperatures 1 to 3 degrees below average.

“The 4-inch soil temperature remained in the 50s through mid-May, and it didn’t consistently top out above 60 degrees until May 20, which is 10 to 14 days longer than usual,” Ford said.

The weather patterns in northern Illinois did a large flip in June.

“In Rockford, over 80% of the days from June 1 to July 31 were warmer than average,” Ford said.

“From June to August, it was the hottest summer on record at O’Hare Airport,” he said. “We didn’t have the extreme heat of 1995 or 1988, but we had consistently above average temperatures.”

A Look Back

The most significant weather event of 2020 was the derecho that occurred on Aug. 10.

“A derecho is a widespread, long-lived wind storm that occurs every couple of years,” Ford said. “But this one was extreme because wind gusts were measured exceeding 100 mph in northern Illinois and estimated to exceed 140 mph in eastern Iowa.”

In addition, the derecho spawned 15 tornadoes in the Chicagoland area.

“The derecho damaged or destroyed 6- to 10-million acres in Iowa and Illinois and almost as problematic as the crop damage was the damage to implements and storage buildings,” Ford said.

“Derechos are not rare in northern Illinois. They occur about every two to three years,” he said. “But because of the incredible wind speeds and the long-lived nature, this event was definitely anomalous.”

The derecho brought the last glimpse of rainfall for the month of August in northern Illinois.

“It was the driest August on record in Moline and the third driest on record in Chicago,” Ford said. “August 2020 was drier than August 2012, but the reason we didn’t see 2012-like impacts was we had wet conditions one and half years leading up to this growing season that helped minimize the crop impacts of this dry period.”

The harvest months were pretty wet in northwest Illinois and a little drier in northeast Illinois, but that did not result in harvest delays as much as in 2019.

“A cold front in mid to late October brought the first fall freeze for northern Illinois about two weeks early,” Ford said. “The late spring freeze combined with the fall freeze resulted in the growing season length 15 to 20 days shorter than average.”

A Look Ahead

A moderate to strong La Niña is likely to maintain through the spring of 2021, Ford said.

“La Niña winters tend to be wetter than normal, but there’s not a lot of relationship with La Niña to temperatures and precipitation in northern Illinois,” Ford said.

“For March to May, there are equal chances of above and below average temperatures,” he said. “There’s a slightly elevated odds of above average precipitation, which is a combination of La Niña and long-term trends.”

Chicago has had three consecutive years with the wettest May on record in 2018, 2019 and 2020.

“The long-term trend is we are much more likely to get a wetter than average spring than a drier than average spring,” Ford said. “There is not a lot of concern for a drought developing before the growing season.”