Chris,
Most of the food crops have narrow temperature bands in which they produce the most. Corn has a real narrow night time temp limit. Corn hates temps at night over 80. There are some interesting studies starting to come out for whole climate belts moving in Australla, GB, and Brazil. I found the study from the U. of Illinois a few months back where they admitted food production was really an unknown area of study in relationship to G. warming.
There was and is a lot of concern here in KS over the transfer of water from the federal lake system to keep the Missouri open this last summer. NE had to shut down some irrigation users on the Republican to ensure they met the NE water level going into Kansas. The river at Salina was for all intents dry this summer and Salina had to limit water usage for the first time since the 50s. No one is sure if it a permanent change or a bump in the road like the 30s and 50s.