The unique problem of desert cities seems to be inappropriate landscaping. Even San Francisco ships its water in from over 100 miles away - not having enough water locally is just a problem of cities in general. The AC story is much worse in a desert city, but the heating story is much worse in cities in cold climates. There's also the benefit that I tend to need my AC when the sun is high in the sky, which aligns perfectly with solar. I live in SoCal and almost never use any heating, even in winter.