Friday, August 10, 2012

US Corn Yields

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.
The eastern counties in the graph account for 85% of the corn that is grown in the US.   While some areas areas are indeed hit very hard (-80 log points is a 55% decline in yields), some areas in the south and northern edge should actually have above normal yields. Overall production in this area is predicted to decline 14% compared to the trend, which is much less severe than what USDA is saying.

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