Photo by A. Miller-Rushing.

Susan Peters, who moved from the East Coast to Tucson, Ariz., a couple of years ago, calls her adopted town an “oasis” — never mind that it only gets 12.6 inches of rain each year on average. “I have a very green, beautiful yard with desert-adapted plants, not the East Coast kind of thing,” she says.

She especially likes her 35-year-old saguaro cactus — the kind “you always see in Westerns,” she says. But if her cactus is ever going to land a starring role in the movies, it’s going to need to grow some arms, and Peters says that could take another 40 years. It’s also going to require water — lots of it, and somehow it doesn’t look as if that’s in the cards. In recent decades, the Tucson area has suffered the grip of a combination of sustained drought and high temperatures possibly unrivaled since medieval times.