I agree that putting this size of a city in the middle of a desert is a fools folly. On the climate thing though the leading theory of why the Anasazi culture ceased to exist was because of a 100 year drought in this same general area. That was just a bit before the internal combustion motor was built. The whole south west including Calif which is in drought conditions has been drying up for a very long time and if you take a look at all the dry lakes in this part of the US that becomes quite obvious.
"Mojave was a much cooler and less arid environment. Portions of what are now vast expanses of desert, were likely shorelines of lakes, streams and marshes, and plentiful vegetation and animal life.
As the climate became hotter and drier, the lakes dried up, the streams receded, and left behind isolated ground water fed springs that contain species found no where else in the world, or "endemic" species. "
Mojave Desert