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How much rain would build back subsoil moisture?

The winter weather patterns engulfing the Midwest this week will be good for recharging subsoil moisture and alleviating drought in some areas — but they’re not enough and not expected to continue through spring.

Holly Spangler

January 12, 2024

4 Min Read
A close-up of hands holding moist soil with grass
SUBSOIL: If the mild winter pattern continues and soils are mostly unfrozen, it will be beneficial for recharging dry subsoils, says Illinois State Climatologist Trent Ford, who acknowledges, “It’s a complicated picture.”Betty Haynes

If you work the land in parts of Illinois, you know it’s dry.

Really dry.

Drier than it really ought to be in January.

Illinois State Climatologist Trent Ford confirms that across parts of western Illinois and most of southern Illinois, particularly south of Interstate 70, conditions range from abnormally dry to severe drought. That means subsoil moisture levels are far below normal, too. Across southern Illinois, subsoil moisture levels all fall in the extremely dry range.

“Maybe 20 inches down, the water tables are pretty far below what they would normally be,” Ford says. “To fix that, we need four to five weeks of abundant precipitation that is soaking in.”

A map illustrating drought intensity in Illinois

How much rain will it take?

In western Illinois, Ford says the Quincy area got 60% of the normal rainfall in 2023, which puts that area at 11 to 12 inches below normal. They need 11 to 12 inches of precipitation to absorb into the ground to get their soil moisture back to normal.

There’s a catch, of course: Drought areas need that quantity of rain, but they need it slow and easy so it can soak in, on unfrozen ground. Winter complicates that.

“It’d be hard to imagine getting enough rain in the style that we want to be able to do that. We’re talking about needing wetter-than-normal weather over the next three months, just to start to make a dent in it,” Ford explains.

A map illustrating soil moisture percentile in Illinois

As any livestock producer can testify, soils are not frozen on top. That means the top 4 to 8 inches can become very wet; then a heavy rain or heavy snow that melts quickly won’t soak in effectively.

“So, in many places, we’re seeing wet soils on top of very dry soils, and we need that to be rebalanced,” Ford says. But it also takes time and consistent rains or snows to get water from the top 8 inches down 50 to 60 inches into the soil.

Temperature complicates that picture, including the frigid air system that’s moving into the Midwest this weekend.

“That’s going to freeze that topsoil very quickly, so any rain on top is not going to be all that beneficial,” Ford explains.

Next 3 months

Ford says what Illinois soils really need is an active jet stream pattern over the next three months, which would bring precipitation systems regularly between now and planting.

“Getting one of these systems every 10 days or two weeks is how we can really make a huge difference in eliminating the subsoil moisture deficits,” he adds.

The three-month outlook isn’t great, however. January, February and March outlooks are showing drier-than-normal conditions across much of Illinois and the Great Lakes region. The next two weeks show better chances of consistent precipitation, but that’s inconsistent with the overall outlook.

A colored map illustrating seasonal precipitation outlook in the United States

Ford is concerned about going into April and May with these deficits. Dry weather is good for planting, but if rain doesn’t arrive after, plants won’t be able to find much moisture deep in the soil. But that’s also what happened in 2023 in many parts of the state, when rain didn’t come until late June, July and August.

“It doesn’t really matter how deep your water tables are if you’re getting the rain you need,” Ford says. “The problem is if the rain doesn’t arrive, then you’re banking on subsoil moisture that isn’t there.”

Changing weather patterns

Ford says Illinois has experienced its share of climate change. While it doesn’t make sense in the context of this story, the overall climate for the state has gotten warmer and wetter over the last 100 to 150 years. Overall, winter has warmed faster than the other seasons, and we no longer get consistent cold air throughout the winter.

“We get bursts, like in 2022 at Christmastime, and like what’s coming this weekend, but it doesn’t happen as often or stay around as long,” Ford explains.

Soils used to freeze and stay frozen for a while, but they don’t as often anymore, as many farmers will attest. It’s a continual freeze-thaw-freeze-thaw cycle throughout the winter.

A colored map illustrating seasonal temperature outlook in the United States

“We’re also getting wetter overall,” he adds. Even though Quincy had its third-driest year on record, the long-term trend is that it’s gotten wetter overall since the late 1800s.

The other trend is in how the rainfall now comes: fewer large rains of 2, 3 and 4 inches, followed by periods without any rainfall, especially in summer.

“We have more periods of drought impacts despite that wetter trend,” Ford says, adding that the changes have some benefits, including a longer growing season.

That’s exactly what many farmers have seen the past two years, where every single month in the growing season was drier than normal, except July and August.

“We’ve had two years now where we’ve accumulated pretty significant rainfall deficits during the growing season, but we got enough rain when we need it the most for the crops to get by,” Ford says. He notes that 2023 is the driest year on record since 2012.

And, as Ford adds, agriculture can work that way — but it’s a lot riskier.

About the Author(s)

Holly Spangler

Senior Editor, Prairie Farmer, Farm Progress

Holly Spangler has covered Illinois agriculture for more than two decades, bringing meaningful production agriculture experience to the magazine’s coverage. She currently serves as editor of Prairie Farmer magazine and Executive Editor for Farm Progress, managing editorial staff at six magazines throughout the eastern Corn Belt. She began her career with Prairie Farmer just before graduating from the University of Illinois in agricultural communications.

An award-winning writer and photographer, Holly is past president of the American Agricultural Editors Association. In 2015, she became only the 10th U.S. agricultural journalist to earn the Writer of Merit designation and is a five-time winner of the top writing award for editorial opinion in U.S. agriculture. She was named an AAEA Master Writer in 2005. In 2011, Holly was one of 10 recipients worldwide to receive the IFAJ-Alltech Young Leaders in Ag Journalism award. She currently serves on the Illinois Fairgrounds Foundation, the U of I Agricultural Communications Advisory committee, and is an advisory board member for the U of I College of ACES Research Station at Monmouth. Her work in agricultural media has been recognized by the Illinois Soybean Association, Illinois Corn, Illinois Council on Agricultural Education and MidAmerica Croplife Association.

Holly and her husband, John, farm in western Illinois where they raise corn, soybeans and beef cattle on 2,500 acres. Their operation includes 125 head of commercial cows in a cow/calf operation. The family farm includes John’s parents and their three children.

Holly frequently speaks to a variety of groups and organizations, sharing the heart, soul and science of agriculture. She and her husband are active in state and local farm organizations. They serve with their local 4-H and FFA programs, their school district, and are active in their church's youth and music ministries.

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