Summary: Rapid drying has occurred across the central Corn Belt since June 1 as virtually no rain has fallen, including most of central and northern Illinois. In addition, high water demand on soils has caused soil moisture to steadily drop in sites across Illinois. Estimates at one location in central Illinois put the water loss from evaporation in the soils and transpiration from plants at 2.4 inches since June 1.
When we get this short-term combination of little rain, high temperatures, and high evapotranspiration rates in summer months, we call it a “flash drought” because conditions can deteriorate rapidly such as they did in the 2012 drought. In my opinion, we are not quite there yet, but we could be if this continues for another few weeks.
Current Conditions and Forecast
Rainfall: Here is the map showing the dryness across the central Corn Belt since June 1. The area shaded gray has had almost no rain at all. Areas in orange have received 0.1 inches or less.
The rainfall departures for June are impressive (below) for being only 12 days into the month. Most of the Midwest is below normal on rainfall. Areas in yellow are 1 to 2 inches down and areas in orange are 2 to 3 inches down.
Water Demand on Soils: Not only are we below normal on rainfall but the loss of water back into the atmosphere (evaporation from the ground and transpiration from plants) has been running high. According to our evapotranspiration (ET) gauge in Champaign, we have lost about 2.4 inches of water to of the ground since June 1. Below is a plot of soil moisture for Champaign. The soil moisture is dropping steadily at the 2, 4, and 8 inches levels (5, 10, and 20 cm). Values of 0.16 to 0.18 in this soil type are pretty close to the wilting point. Other parts of the state are showing a similar pattern of steady decline.
The units used here are water fraction by volume, which is a little wonky. So “0.16” means that at a particular point in the profile only 16% of the soil is made up of water. Plants have a hard time extracting that last 10 to 15 percent of the water in the soil, as a result the plant will wilt. Soils in Illinois can hold upwards to 50% water by volume.
High ET rates: The driving force for the high rates of evapotranspiration (ET) has been a combination of high temperatures (map below), clear skies, relatively low humidity (at least by Midwest standards) and breezy conditions. The last time I saw conditions like this was at the beginning of the 2012 drought.
Will It Rain? Yes, according to the NWS, there are chances of rain this week in Illinois, starting on Tuesday. Here are the potential 5-day totals, although the actual totals will likely be less. We need at least 1 to 1.5 inches of rain per week to hold our own with soil moisture. We need 2 or more inches per week for a while to catch back up from the recent dryness. One sign of impending drought is when the actual rainfall amounts fall far short of the forecast, indicating that the models are missing the local source of atmospheric moisture as the ground becomes parched.