Dry Conditions Persist for this Spring in Illinois, Illinois State Water Survey

Illinois Drought

Conditions Dry in Southern and Eastern Illinois This
Jim Angel - (217) 333-0729, Fax: 217-244-0220, jimangel@illinois.edu
Lisa Sheppard - (217) 244-7270, Fax: (217) 333-6540, sheppard@uiuc.edu

"Southern Illinois south of I-70 is fast approaching a three-month severe drought," says State Climatologist Jim Angel of the Illinois State Water Survey, a division of the Illinois Department of Natural Resources.

After a near normal winter in terms of precipitation, this spring has been dry in both southern and eastern Illinois.

"Based on ISWS research of past droughts in Illinois, a region experiencing less than 45 percent of average rainfall over a three-month period is considered to be in a severe drought. As of May 18th, southern Illinois is close to that point (Figure 1). This region needs on average a half of an inch or more of rain for the rest of May to stay out of the severe drought category. Unless the two southernmost crop reporting districts receive more than a three-quarters of an inch of rain in the next two weeks, it will be the driest March-May period since statewide recordkeeping began in 1895," says Angel. The east-southeast crop reporting district only needs a quarter of an inch in the next two weeks to avoid being the driest March-May since 1895.

Although the rains of May 17-18 in southern Illinois will provide some local relief, the rains are not widespread enough to help the whole region. "Large portions of Illinois south of a line from St. Louis to Springfield to Kankakee are still at 66 to 67 percent of average for the March-May season, leaving them at just above the threshold of 60% of average rainfall for a moderate three-month drought. This dryness ties into a larger area of dry conditions in southern Missouri, most of Indiana, and western Kentucky. Meanwhile, near to above-average conditions persist in northwestern Illinois," continues Angel.

Because soil moisture was in good supply in March, the dry weather has only affected the upper soil layers. Based on measurements from the Water and Atmospheric Resources Monitoring Program at ISWS, the latest soil moisture observations for May 15 show soil moisture dropping below 50% of average in the top 6 inches for the area to the south of Interstate 70. Soil moisture at the 6-20 inch layer in the far southeastern region of the state has dropped to less than 50% of average as well. Local differences in soil moisture may exist based on rains after May 15 measurements as well as soil type, vegetation, and slope.

Southern Illinois has felt the impacts of diminished moisture in the top soil layer in the form of a lack of germination in planted crops, a slowdown of planting, reduced herbicide effectiveness, and increased irrigation. Soil moisture in deeper layers remains in good shape for most of the state.

Streamflows also have responded to the low rainfall in Illinois with lower than average flows in southern and eastern Illinois. Gages on the Cache, Little Wabash, and Saline Rivers in southern Illinois are approaching their record lows for May unless significant rains reverse the trends.

The May 17 outlook for June and for the 3-month period of June-July-August from the National Weather Service call for equal chances of above, near, or below-average rainfall in Illinois. "Rainfall patterns can shift dramatically in Illinois. After a dry spring last year, most of Illinois received 2.5 to 3 inches of rain in the last half of May. So it's not too late to reduce or reverse some of the impacts seen so far," concludes Angel.

Illinois State Water Survey

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Champaign, IL 61820-7463

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