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Will 2010 mirror 1983 in the Corn Belt?

In 1983, spring and early summer was wet and cool -- as many as 200 growing-degree days (GDDs) behind normal in some parts of the Corn Belt.

This spring and early summer have been wet and cool, with some spots around 100 GDDs behind normal. June was the wettest month on record, statewide, for Iowa, recent numbers show.

In 1983, once the calendar turned to July, the faucet turned off and temperatures took off, exerting serious stress on the Midwest's corn and soybean crops.

"The 2 years 2010 and 1983 have a lot in common so far, at least at Ames, Iowa. I haven't analyzed other locations, but Ames was not typical of the region either year," says Iowa State University Extension climatologist Elwynn Taylor.

"The 1983 heat in July was accompanied by greatly diminished rain after the first week of July until the last week of August. The temperature stress -- hours of temperature exceeding 86 degrees Fahrenheit -- reached 260 by the last week of August. Normal temperature stress is 65 for the period," he adds.

With trends like these lining up, it's got Taylor wondering whether July 2010 will unfold similar to that month in 1983. The biggest factor to watch moving forward, he says, is the Southern Oscillation Index, or the measure of oceanic weather patterns developing there and how they influence what happens in the Midwest. The current trend foreshadows a possible shift to a hot, dry pattern.

"The May through June 2010 switch from El Nino to La Nina...does present an historical probability of an increased incidence of stressfully hot days during the 2010 season," Taylor says.

What's this shift mean for yields? In short, it could mean 1983 all over again. "The statistical chance that it could result in a U.S. corn yield below the trend (below 160 bushels per acre) is near 70% as opposed to a 50/50 chance on an average year," Taylor adds.

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