On the issue of rain fall in California, I'm reminded of "However, imagine that California had to get its entire water supply of 35 million acre-feet per year by desalinating sea water at the Santa Barbara price. This would come to $70 billion per year, which is on the order of ten percent of the state's GDP. We'd survive, but it would be a blow to our standard of living, and the arguments about whose fault it was and how the cost should be allocated would be exciting."

from http://www-formal.stanford.edu/jmc/progress/water.html

which agrees with you about political unrest, but not about famine. Before I read that, I assumed that desalination was only for drinking water, and far to expensive for agricultural use. That is probably about right for poor countries, but rich countries might get through the total failure of the rains without famine (and without WW3).