Ag Weather Forum

Derecho and Drought Truly Damaged Yield

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Estimated Iowa corn yield after drought and derecho in 2020 is 15 percent lower than USDA's August estimate. (DTN photo by Matt Wilde)

We continue to see the damaging impact of the August 10, 2020 derecho and western Corn Belt drought during the last half of the 2020 summer. The total U.S. corn crop in the November USDA production estimate came in at 14.5 billion bushels, around 5% lower than the August estimate. National corn yield is also estimated some 3% lower than the projected record yield in August of almost 182 bushels per acre; the November number is 175.8 bushels per acre.

A big reason for that national decline, of course, is the drawdown in Iowa production after the August 10 derecho windstorm and drought during the summer. Iowa's November corn production estimate of 2.34 billion bushels is 15 percent below the August estimate (details which were in the mix as of August 1, before the derecho hit). The Iowa yield estimate, 184 bushels per acre, is 9% below the August estimate of 202 bushels per acre.

These are sharp declines. And, the situation brought on in operations where the derecho and drought made for a one-two combination sparks the grower memory bank to the dismal 2012 heat and drought year. At least, these experiences brought that year to mind for central Iowa producer Grant Kimberley. In an email conversation, he shared the following details.

"I think the derecho and August dry spell combination this year did far more damage to yields then we saw from the 2012 drought. This is the worst corn year by percentage decline I can remember. We got hit by another derecho in 2011 and prevent-plant and late-planting issues in 2013 as well. Those all really hurt our yields, too, but this year takes the cake."

Kimberley's corn yields have steadily declined as well. "We don't have our final yields all calculated yet, but the trend has been lower and lower," he noted. "Early harvest was in the 150s and 160s with a few 180-200 bushel per acre (bpa) fields. But quite a few lately have been in the low 100s. Not to mention a few fields that got zeroed out. I would be surprised if this year doesn't end up worse on average than the 2012 drought year, or it will at least be close."

2012 was a record hot and dry year in much of the central U.S. To challenge its impact would take a record event -- or two. That happened and the results are coming in.


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Bryce Anderson

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