Unique Weather, A Factor in Record Yields of All Major Crops in Illinois and the Midwest in 2004, Illinois State Water Survey

Press Release

For Immediate Release March 10, 2005
Unique Weather, A Factor in Record Yields of All Major Crops in Illinois and the Midwest in 2004
Stan Changnon - (217) 244-0494, Fax: (217) 586-5691, schangno@uiuc.edu
Eva Kingston - (217) 244-7270, Fax: (217) 333-6540, eva@sws.uiuc.edu

(Champaign) “Near perfect growing season weather conditions over Illinois and the rest of the Midwest in 2004 resulted in record yields much greater than past records for all crops and above expectations of crop experts. Never before have corn, soybeans, sorghum, and alfalfa hay all achieved record yields in the same year,” says Stan Changnon, chief emeritus of the Illinois State Water Survey (ISWS) and adjunct professor of geography at the University of Illinois at Urbana-Champaign.

“Planting during the 2004 growing season was early. Summer temperatures were below normal with no hot days. Rainfall was adequate. Crop yield predictions issued during the growing season and up through August 2004 did not anticipate the high magnitude of the corn and soybean yields that actually occurred across the Midwest, however,” says Changnon.

Sophisticated crop-weather models relying on daily temperature and rainfall values of 2004 also did not calculate yields as high as the actual yields. Predictions and model-generated yields were 7–15 percent lower than final corn yields for the 11 Corn Belt states, 15–33 percent lower than final soybean yields of the Midwest. Changnon says those outcomes help reveal that weather conditions critical to generating extremely high yields of all Midwestern crops were not detected during 2004. He and his son David, a geography professor at Northern Illinois University in DeKalb decided to take a closer look at the weather conditions during 2004.

That search revealed an unusually high number of sunny days occurred, facilitating photosynthesis. Analysis provided strong evidence that the much above average frequency of summer days with clear skies was a critical, beneficial factor for all Midwestern crops.

“When a large number of clear days occurred in most previous summers, conditions were hot and dry with much above average temperatures and below average rainfall. Temperatures in 18 of the 33 summers between 1888 and 2003 with frequent clear skies averaged between 1.2°F and 4.5°F above the long-term average,” says Changnon.

Summers with frequent clear skies, well below average temperatures, and above average rainfall only occurred in two years during the past 117 years, 1927 and 2004. Skies were clear on many more days in 2004 than in 1927, and June and August rainfall amounts in both years had different magnitudes. Thus, the 2004 weather conditions were anomalous.

Summers with below average temperatures in all three summer months, as in 2004, occurred in 18 previous summers between 1888 and 2003. Sky conditions during those cool summers were mostly cloudy, quite different than in 2004.

“A climatological evaluation revealed that summer 2004 conditions were unlike any experienced during the past 117 years,” says Changnon. Sunny, cool conditions in 2004 were due to 20 cold fronts from Canada that crossed the Midwest, followed by strong high-pressure systems persisting for several days. Each such intrusion brought temperature decreases of 5°F to 15°F, and then a series of several clear days. High-pressure centers dominated the atmospheric circulation and kept warm, stationary fronts with their attendant penetrations of warm, moist air masses away from the Midwest.

“The atmospheric circulation pattern during summer 2004 was unusual, but these conditions and their crop impacts are not considered indicative of those expected with a change in climate due to global warming,” says Changnon.

The widespread similarity of 2004 summer conditions across the 11-state Midwest, a highly unusual event, was a key factor in setting new national yield records for corn and soybeans. The combination of April–September weather conditions also led to record high yields for all other major crops, something that had never occurred for all crops in the Midwest in the same year.

The report detailing the study is available from the ISWS (http://www.sws.uiuc.edu). The research was conducted as part of the weather-climate impacts program of the Midwestern Regional Climate Center (http://sisyphus.sws.uiuc.edu/index.html) and the ISWS climate program.

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