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Davis Kitchens Cabinet Sales Administrative & Professional City of Benson Planning & Zoning Director Tucson RegionBy 2050, drought affecting CAP seenClimate change, other factors may cut flow sharply, study says
Arizona Daily Star
Tucson, Arizona | Published: 04.24.2009
Picture the Central Arizona Project as a half-empty canal snaking through a hotter, drier Arizona desert.
That image is likely to become a regularly occurring reality by 2050, says a new study released by the Scripps Institution of Oceanography in San Diego. It warns of reduced runoff caused by rising temperatures and drought that could reduce the river's long-term flow from an average 15 million acre-feet per year to only 11 million to 13.5 million acre-feet annually.
That flow could drop even further to as little as 6.5 million to 8 million acre-feet annually if the effects of climate change on the river are compounded by a return to historical flows rather than those seen during the 20th century — generally agreed to be the wettest or second-wettest century of the last millennium.
For the $4 billion CAP, water deliveries could regularly be slashed by one-third to one-half of the current 1.5 million acre-feet if the study's forecasts prove true, said David Modeer, the project's director. An acre-foot is 325,851 gallons, enough water to serve up to three families of four for a year.
Researchers in Arizona need to do more studies to detail the local effects of climate change on the Colorado River, as well as on the Salt River, Modeer said.
Still, Modeer does not take issue in general with the Scripps study's conclusions. That's in sharp contrast with last year, when CAP officials rebuked a study from the same Scripps researchers warning of a 50 percent chance that Lake Mead and Lake Powell on the Colorado would go dry by 2021.
"We are certain that there will be impacts to the flow in the Colorado River," Modeer said. "What the actual impacts will be, we are not sure."
The study's co-author, Tim Barnett of Scripps, said three factors are at play for the Colorado River — all headed in the wrong direction. Those factors are the effect of human-induced climate change; the return to historical flows due to natural cycles; and continued population growth in the Colorado River Basin, where about 27 million people now live.
"We are rapidly coming to the point where people will have to make hard decisions: freeze the size of Phoenix or say we don't want more agriculture in the West," Barnett said. "From most local politicians I talk to, they don't want to touch this with a 10-foot pole."
But Modeer said that people shouldn't think twice about moving to Arizona because of this study. With enough effort to perfect computerized forecasting models, "I think we can do the right decisions and make adequate investments to ensure an adequate supply," he said.
That will require conservation and additions to existing supplies by desalinating salt water, transferring farms' water to cities and other measures," he said.
About the CAP
The Central Arizona Project is a large system of canals that sends Colorado River water 336 miles from Lake Havasu City to Tucson.
Construction of the project took 20 years and cost $4 billion. Although construction began in 1973, planning and lobbying for the project began more than 50 years earlier.
Sources: CAP, Star news archives
Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com.
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