If less rain means that the relative deserts of California and Arizona can't be irrigated/subsidized as heavily, the resulting price increases will shift agricultural production back to more natural locations in the Midwest. There was once a dairy industry here, for one thing. We couldn't compete with the desert alfalfa of the Salt River Valley, but then again maybe their advantage wasn't an environmentally sustainable one. It requires a certain perspective to bemoan the fact that deserts aren't great places for agriculture.