Other way around. Humans and pre-human hominids evolved in a more confined region of the world for an extremely long time, and they left recently enough that they still instinctively prefer the climate of that region.
Prehistoric spread was driven by other factors that were more important than climate preference. But that doesn't eliminate climate preference, and all else equal humans will act on that preference.
Oh, I see, I think: you are saying that we have preserved a preference for our ancestral habitat, and that has motivated recent migration into arid areas? Maybe so; we still have some physiological adaptions for warm climates.
When it comes to agriculture in the desert, which is still the major reason why the snowpack shortfall is a matter of concern, the motivation seems more economic: crops grow very well in sunny climates, so long as you can give them adequate water - and we could, for a while, but probably not sustainably.
Modern humans came frome the Ethiopian plateau right? So low of 75F high of 80F sort of thing. High altitude equatorial. Bogotá is similar but cooler. As is Quitó. Much of coastal Europe and west coast North America is a decent approximate.
Coastal Europe has considerable variation and the west coast of North America even more so, but what is of more relevance to the snowpack issue is that most of the lower Colorado basin is quite unlike what humanity's home was like prior to our global spread.
Prehistoric spread was driven by other factors that were more important than climate preference. But that doesn't eliminate climate preference, and all else equal humans will act on that preference.