SALT LAKE CITY — If the West continues to heat up and dry out, odds increase that the mighty Colorado River won’t be able to deliver all the water that’s been promised to millions who rely on it for their homes, farms and businesses, according to a new study.
Less runoff — the snow and rain that fortify the 1,400-mile river — caused by human-induced climate change could mean that by 2050 the Colorado won’t be able to provide all of its allocated water 60 percent to 90 percent of the time, according to two climate researchers at the Scripps Institution of Oceanography at the University of California at San Diego.
The more parched the landscape, the more difficult the choices will be for those with dibs on the Colorado’s water and those in charge of divvying it up, said Tim Barnett, lead author of the study.
“The dry year scenarios in the future are going to be absolutely brutal,” he said.
Barnett and fellow Scripps scientist David Pierce made waves last year with a study saying there’s a 50 percent chance that Lake Mead, the reservoir created by the Hoover Dam, could run dry by 2021.
They teamed up on the latest study to predict when the river — under different climate scenarios predicting 10 percent to 30 percent reductions in runoff — will be unable to fully meet all of the demands put on it.
The results were published Monday in the journal Proceedings of the National Academy of Sciences.
“Without numbers like this, it’s pretty hard for resource managers to know what to do,” Barnett said.
The Colorado is a lifeline of the southwest, flowing through seven states and into Mexico and quenching the thirsts of some 27 million people who use it to irrigate crops, water lawns, produce drinking water and operate businesses.
Drought has already stressed the river. The problem is being compounded by growing populations demanding more water and the expected effects of climate change, said Brad Udall, director of the University of Colorado’s Western Water Assessment.
“We’re on a collision course between supply and demand,” Udall said.
The Bureau of Reclamation, the federal agency that plays a key role in how the river system is managed, has used a different set of calculations than the Scripps researchers to reach a similar — though less dire — prediction, according to Terry Fulp, the agency’s Nevada-based deputy regional director for the Lower Colorado.
His agency’s calculations predict the Colorado could run short of water 58 percent to 73 percent of the time by 2050.
There’s room to quibble over percentages, Fulp said, but the overriding point remains.
“We’ve got some serious issues to grapple with,” he said.
Under conservative climate change scenarios in the West, Barnett and Pierce found decreases in runoff could short the Colorado River by about 400,000 acre feet of water 40 percent of the time by 2025. That’s equivalent to the amount of water needed to supply 400,000 to 800,000 households.
Those figures double later in the century, according to the Scripps researchers.
The signs point toward tough decisions about who will get less water. Agricultural operations use about 80 percent of the water taken out of the Colorado, Barnett said. He knows the arguments, though: Shorting farms could drive up food prices. Curbing development in cities and suburbs will make developers unhappy. Whatever the case, he said, some decisions need to be made soon.
“The actions that need to be taken aren’t going to be fun,” Barnett said. “It’s not going to be life as usual.”
But, Barnett and Pierce said, it isn’t too late to buffet some of the harshest effects.
Measures such as conservation and water exchanges, which can require upfront investments and flexibility, could play a key role in avoiding some of the biggest shortfalls, they said.
In 2007, officials from the seven states that get water from the river — Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming — and then-Interior Secretary Dirk Kempthorne signed a far-reaching agreement aimed at conserving and sharing the scarce resource. The 19-year plan formalized rules for cooperating during the ongoing drought.
Meanwhile, researchers will continue gathering information on climate change and looking for ways to keep the Colorado functioning — albeit with a new set of climate-driven rules.
“It really depends on how innovative people get,” Fulp said.
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On the Web
Proceedings of the National Academy of Sciences: www.pnas.org