Ag Weather Forum

Midwest Dryness Growing; Yield Loss Concern Increases as Moisture Decreases

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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A large swath of the Midwest has had well under 50% of normal precipitation since early July; Illinois has had deficits of near 90%. (Midwest Regional Climate Center graphic)

OMAHA (DTN) -- For a large area of the Midwest, the rain valve that had been wide open in spring now has been closed with an extra vise-grip turn. From eastern Nebraska to central Ohio, rainfall during the early July to early August time frame has run well under 50% of normal. In fact, a large part of western Illinois has had a rainfall deficit of close to 90% below normal.

This sharp change in precipitation means crops, which developed root systems based on a full soil moisture profile, do not have the root structure to dig deeper. "I doubt that the root structure is 4 feet deep," said University of Nebraska-Lincoln Extension educator Tyler Williams. Williams has seen dryness take hold in eastern Nebraska. "Shallow rooting is a problem," he said. "The first part of the growing season, the roots didn't have to go down. The roots grew to the water."

Williams has seen the greatest stress from recent dryness in corn. "There's a lot of corn stress; not as much in (soy)beans," he said. "Beans have had lower water use up to this point."

The recent drier trend in the Midwest coincides with the ending of a weak El Nino Pacific Ocean temperature event and a sharp cooling of the eastern Pacific waters. DTN Senior Ag Meteorologist Mike Palmerino has been cataloguing the eastern Pacific Ocean temperatures for more than 30 years; his latest update found a lowering of more than a half-degree Celsius during July. "My SST (sea surface temperature) departure for the month of July is minus 0.4 degree Celsius," he said. "It was plus 0.3 in June. That is a major decline."

Palmerino sees a tie-in between the sharp eastern Pacific Ocean cooling in July and the drier trend in the Midwest. "A change in the sea surface temperature departure can be just as important as what the departure is," said Palmerino. "We have seen in the past that if you are looking at significantly falling sea surface temperatures in the Pacific, that can dry out the Midwest." Two showcase examples are the years 1988 and 2010, when corn yields were well below the previous year's output. Both those example years featured the Pacific transitioning quickly away from El Nino to eventually strong La Nina events. While La Nina is not forecast to develop in the Pacific this late summer, the sharp change and the quick drying of Midwest weather, has crop stress increasing due to shallow root formation.

And, when the season is all done, Williams looks for a new detail to factor in as crop performance is evaluated. "The dryness adds another line to the matrix of what defines a crop yield in a given year," he said.

Bryce Anderson can be reached at bryce.anderson@dtn.com

Follow him on Twitter @BAndersonDTN

(ES/CZ)

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