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Long-term Increasing Temperatures, Intense Rain Could Threaten Iowa Crops

Amy Mayer/IPR file

Human-caused climate change will trigger more intense rain and more frequent heat waves in the Midwest, according to a recent climate assessment.
The Fourth National Climate Assessment report by U.S. Global Change Research Program projects high temperatures increasing by 7 degrees by 2050 and more intense rain for the Midwest by 2050 to 2100.

Iowa State Climatologist Justin Glisan said the state is already seeing higher intensity rain events. For example, the City of Ankeny in Polk County got 10 inches of rain in a three-hour period this summer.


“What we’re getting are more localized and smaller temporal scale, extreme event type thunderstorms in which these thunderstorms form in the specific part of the state and they pop up and just rain out all this rain,” Glisan said.

Glisan says this heavier, more localized rain causes more soil runoff.

Gene Takle, a retired Iowa State University professor who contributed to the report, said it also means farmers will have to adapt their growing season and will have smaller windows to plant between heavy rain events.

“Farmers can’t get into the field to plant if the soil is wet,” Takle said. “You have to be careful with big machinery on wet soils because you can compact the soil and that’s detrimental to crop growth.”

Wetter years and soil erosion are things Keota soybean producer and American Soybean Association President John Heisdorffer said he prepares for. Heisdorffer uses between 40 to 50 terraces to hold water back from affecting his crop.

But Heisdorffer said when he first started farming 47 years ago, things were different. Back then, he would land plow the ground, turning soil over 6 inches to 8 inches deep in a field.


“That is a huge change because every time you work that ground up that way, you leave it vulnerable to a three to four inch rain that is going to make that dirt move, so you’re going to lose that soil,” Heisdorffer said.

The rains seem more intense than they used to be, he said. 

"A crop likes about an inch a week of rain. I'm talking about perfect conditions. That's what a crop would like to have," Heisdorffer said.

Heisdorffer said he had no problems planting in mid-April this year, but it ended up being a dry year for his crop, which cost him some yield.

“Since then we’ve had rains, but not a huge amount,” he said.

Rising temperatures in the Midwest can also plague crop growth. The report lays out two possible warming scenarios over mid- and late-century to show possible outcomes for temperature. Under the highest scenario, temperatures could rise by more than 9 degrees between 2005 and 2100.

The warmest day of the year is expected to increase by 7 degrees, and a five-day one-in-10-year heat event is expected to be 13 degrees warmer by then.

“We’re going to be seeing temperatures that are going to really be a factor in whether corn is really flourishing in this state,” Takle said.

Takle said temperatures above 95 degrees make it difficult for corn to grow.

For soybeans, 80 degrees is an ideal growing temperature, Heisdorffer said.

“You can get by with 80 to 90 degree days and...as long as you get a little rain all along, you’ll get a crop,” he said. “When the temperature raises and you get into that 100-degree days, that really takes its toll on the crop.”