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Wednesday, May 11, 2016

Summer Weather, El Niño, & Corn Yields

ifr160513–111
Summer Weather, El Niño, & Corn Yields
Scott Irwin, Agricultural Economist - University of Illinois

The agricultural economists at the land grant university in Illinois have gone through 56 years of weather data to see if there is any connection between the current El Niño event and trend yields for corn. Todd Gleason has more…

The ag economists at Illinois say the trend…
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The trend yield for corn has been going up 1.8 bushels per yer for about 50 years say the number crunchers from the University of Illinois. It means, under normal weather conditions with a little adjustment upward, this year’s corn crop should average 166.2 bushels to the acre nationwide.

U.S. Average Corn Yield, 1960-2015
U.S. Average Corn Yield, 1960–2015

The 166.2 is the norm, but it lives within a range that would be indicative of really good years like 2004 and really bad years like 2012 says U of I’s Scott Irwin.

Irwin :14 …doesn’t happen every year that we call El Niño.

Quote Summary - And now what we want to ask is if we should skew our expectations of this risk given this outside factor that doesn’t happen every year that we call El Niño.

ILLINOIS’ research suggests the answer to this question is a qualified yes. The qualification is that the El Niño event is measured strictly as an effect of water temperature in the Pacific Ocean near the equator and that only the most extreme of these events, those a full degree or more centigrade above the norm for three months running, would be considered strong enough to regularly have a real measurable impact on U.S. crops.

Irwin :39 …we called the pre-season periods for corn production.

Quote Summary - The warmest one, to date, was 1997/98 and it peaked at 2.3 degrees centigrade above normal. So if you take the same period and you estimate trend yields going back to 1960 there were 11 El Niño episodes where we were at least one centigrade degree above normal and, this is the key, we filtered the data so that these spikes had to occur in what we called the pre-season periods for corn production.

This would be from September to March prior to the crop year. It is exactly what has happened this year and the spike is more than two degrees centigrade. It’s a really big one.

Irwin :14 …four to five bushels below trend.

Quote Summary - What we find is, in these big spiking El Niños that occur in the pre-season period, that corn on average is about 4 to 5 bushels to the acre below trend.

Having said that, Irwin points to a large range of occurrences from 11 bushels above trend in 1992 to 23 bushels below trend in 1982. 1988 and 2012, the two worst drought years, also count under this construct.

Trend Deviations for U.S. Average Corn Yield, 1960-2015
Trend Deviations for U.S. Average Corn Yield, 1960–2015

The model used very reliably predicts summer heat waves, however, it is not so great at determining the amount of rainfall. Recall the reference Irwin made to the 1997/98 pre-season El Niño, the largest on record, similar to this year. The national corn yield was 3 bushels to the acre above trend. The heat wave came, it was just very last in August and early September after the corn crop had been made.