It all began last December and ends with the recent rains of the past two months.
Essentially, the winter of 2023-2024 was extremely mild. Even though everyone remembers the one week of polar vortex below freezing weather, most of the winter was extremely mild. According to WGN Weather this past winter “ranks 7th warmest of the past 153 years here and is posting a temp surplus of 6.1 degrees to date [as of late February].”
As a result, the area did not experience a hard frost in the ground. The Illinois State Climatologist, on average, the frost depth is 36 inches and can remain in the subsurface soil until mid-April or early-May. There was little to no lasting hard freeze in the ground this entire winter.
Usually, a deep, long-lasting hard freeze in the ground causes snowmelt and early spring rains to run off the land because the soil is essentially impervious. With this year, however, all the (little) snowmelt and all the (weekly) rains were able to fully saturate the surface and subsurface soils creating the ponding and runoff that we aren’t used to seeing at this time of year.
According to the National Weather Service, a total of five inches of rain has fallen since February first. In addition, the unseasonably mild February and early March brought people outdoors at a time when they are usually still locked away indoors. Again, seeing things they aren’t used to seeing at this time of year.
Lastly and most importantly, over the past 4 weeks of rain and super saturated soils, there have been no leaves on the trees and plants to draw out the moisture from the ground. On average, a mature oak tree can transpire about 100 gallons of water per day. Imagine the 10 to 15 trees around your house pumping out 1,000 to 1,500 gallons per day.
Furthermore, leaves on mature trees and in the understory intercept rainwater and prevent it from reaching the ground. See where this is headed? You guessed it, no leaves = no interception and the full rain event, no matter how small, is ending up on the already saturated ground. The graphic below illustrates the complete evapotranspiration process that tree leaves provide us.
Photo Credit: https://www.purdue.edu/fnr/extension/purdue-landscape-report-how-do-trees-use-water/
Without this ecosystem service fully operational, it will take a few weeks for things to dry out, even on warm, sunny, and windy days (which provide the energy to drive the process of water evaporation).
Add it all up and it’s no wonder our yards are so wet. But help is on the way. Be patient, put on your galoshes, and get ready for a brilliant display of May flowers!