With all of the argument about the effects of global warming, it seems one thing is clear whatever the cause.
Weather patterns will change. Areas that once had low rainfall will have increases others reductions. While this may have always been the case, people and population centers have followed the water. The trouble these days is that many big cities were built around water supplies as though they would always be there, and you can't just move a city, perhaps only the people.
Modern 'civilization' may have just accelerated the change.