Forecasting Corn Yields

My colleague Wolfram Schlenker has developed forecasts for this year's corn yield based on weather through August 6.  We've been considered pessimists by some, since this model predicts really big declines in crop yields under projected climate change.  But this year we're the optimists: our model predicts a US yield only a 14 percent below trend. That's bad, but it's not nearly as bad as USDA's forecast last Friday of 25 percent below trend.

I'm replicating his post so you don't have to click through:
USDA today announced its forecast for corn yields. It might be fun to compare those forecast to one using a statistical model of corn yields that my colleague Michael Roberts and I have developed. It uses only four temperature variables (two temperature and two precipitation variables - if you want to read more, here's a link to the paper). The temperature variables in 2012 are shown here.

All weather variables in the model are season totals for March 1st - August 31st. The following graph combines actual weather observations for March 1st-August 6, 2012 with historic averages for August 7th-August 31st in each county.  Once the actual weather for the rest of August is realized, the predictions will obviously change dependent on whether it warmer or cooler than usual.


  1. I presume you also used the prediction/categorical variables acreage irrigated and acreage non-irrigated.
    Irrigated land is robust against drought, irrigated land's yield would not change with drought, so irrigation is the ultimate insurance.

    Indeed, the largest U.S. aquifer, the Ogalla Aquifer, more aptly called the Nebraska Aquifer, replenishes itself in eastern Nebraska. Just over the boarder in Iowa and Kansas, the land can parch. As a result, irrigated land produces the same in droughts and in rain, while prices increase in droughts. Looking at irrigated corn returns over 20 years could be like a hedge fund looking at returns over 20 businesses.
    This year showed the value of such sustainable irrigation as farm land prices for eastern irrigated Nebraska land increased more than any other region -- 38 percent -- to $9000 per acre.

    At any rate, the presence of irrigated land moderates decreases in U.S. production,
    while more corn/soybean profits for the year go to irrigated land.

  2. Mr Burt; it is my understand some of this year's irrigated crops were damaged by temps over 95F during pollination...

  3. Jameson, this model focuses on the mainly non-irrigated land east of the 100th meridian. West is all irrigated, and the folks in Nebraska are especially blessed with the Ogalla.

    Most of the damage from extreme heat seems to come from higher vapor pressure deficit, associated water stress from elevated evaporation and transpiration. But it appears extreme heat damages even irrigated crops, but nowhere near as badly as non-irrigated land. On irrigated land there can be pollination issues, greater pest pressure, reduced yield from accelerated maturity and perhaps other issues.


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