MARY LOUISE KELLY, HOST:

A 23-year megadrought is pushing some farmers in the Southwest to the brink. We're going to hear from the first place where farmers have been totally cut off from Colorado River water - central Arizona. As NPR's Kirk Siegler reports, the crisis is renewing questions about the viability of growing thirsty crops in a desert.

KIRK SIEGLER, BYLINE: Will Thelander has heard it all before. Yes, this harsh and hot patch of ground south of Phoenix that he farms is a desert. And yes, farms gulp up about 80% of all the water in the Colorado River Basin. But he's tired of all the shots.

WILL THELANDER: And they're like, well, cities use less water. OK, what has a bigger environmental impact - you know? - an open farm like this or the city of Phoenix?

SIEGLER: In Phoenix, you'd hardly know there's an historic drought. They still have water. But this year, farmers here in Pinal County had their Colorado River pumps shut off, and Thelander is fallowing half of his land. And at 35 years old, he's starting to get worried about the future of farming in the Southwest.

THELANDER: They didn't magically pick a desert where it was hard to get water to to start farms. There's a reason all of this was done.

SIEGLER: He means as long as you have reliable irrigation, you can grow all kinds of things in the desert Southwest, ironically, because it barely rains. From October to May, it's warm and sunny, and storms don't ruin crops.

THELANDER: You can't just go, well, it's the desert and they're out of water, so we'll grow food elsewhere. Well, these industries have taken 50 to 100 years to establish. You don't just go, hey; we'll grow elsewhere. It's complicated.

SIEGLER: Fifty to 100 years ago, people thought the Colorado River was infinite - America's Nile - so they built a complicated and elaborate plumbing system of canals to create an enormous agricultural economy in the desert.

(SOUNDBITE OF DOCUMENTARY, "THE STORY OF HOOVER DAM")

UNIDENTIFIED PERSON #1: Thus, the first thunders of man's determination to conquer the Colorado River...

SIEGLER: When the Hoover Dam was built and Lake Mead filled, cheap, federally subsidized water allowed farmers to grow pecans in New Mexico, alfalfa and cotton in Arizona, greens and citrus in California.

(SOUNDBITE OF ARCHIVED RECORDING)

UNIDENTIFIED PERSON #2: And so a vigorous modern culture replaces that of a bygone age in the Southwest. The wastes of strung native growth become vast irrigated citrus farms.

SIEGLER: Well, that almost mythical river doesn't exist anymore, says Jack Schmidt, who runs the Center for Colorado River Studies at Utah State University.

JACK SCHMIDT: There have been warnings and fears about whether or not there was enough water before the scepter of climate change ever reared up.

SIEGLER: Schmidt says farmers in central Arizona, particularly, were always warned this day could come. Under the century-old river law, they're last in line for irrigation in a megadrought. Ted Cooke manages the Central Arizona Project. It's a federal canal system built in the '60s so Arizona farmers could tap into excess Colorado River water.

TED COOKE: We are two years or less away from not being able to get any water past the dam in Lake Mead. That's...

SIEGLER: That's pretty extraordinary...

COOKE: It's pretty extraordinary. So something has to be done.

THELANDER: Something is going to have to change, or the Southwest is going to lose their agriculture.

SIEGLER: What farmer Will Thelander is doing for now is planting a new desert crop called guayule. It requires a quarter of the water that his traditional cotton and alfalfa do.

(SOUNDBITE OF TRUCK DOOR SLAMMING)

THELANDER: So, like, I'm hoping on this crop right here that it's going to rain.

SIEGLER: OK.

THELANDER: And I don't water this for another three weeks because it's a desert crop, and then I...

SIEGLER: Guayule produces a natural desert rubber. Right now, only 74 acres of Thelander's farm has been converted to it.

THELANDER: But if the economics continue to work out, you know, I think this could be a huge crop for the Southwest.

SIEGLER: A crop he thinks could make farming sustainable here in a hotter, drier world. American tire companies are already pumping money into its cultivation. Kirk Siegler, NPR News, Phoenix.

(SOUNDBITE OF FUGEES SONG, "READY OR NOT") Transcript provided by NPR, Copyright NPR.