Peter O'Dowd

The Arizona city already logs more days over 100 degrees than any U.S. city, and climate researchers predict Phoenix will grow hotter still in the coming decades. Planners are taking the projections seriously, and are looking for ways to adapt the city and its residents to a hotter, drier reality.

With many boomtime developments now just dusty wastelands, Sun Belt suburbs like those outside Phoenix are shifting gears. Some planners argue for a radical option called "smart decline" — letting empty lots go back to nature and even, in some cases, tearing down infrastructure.