Colorado River Reservoirs Running Dry

There's a 50-50 chance that the Colorado River system will dry up as early as 2012, according to one analysis. Another says the reservoirs will stay viable longer, but face that 50-50 annual chance of drying up around 2057.

Photo: Scripps Institution of Oceanography, UC San Diego

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Parts of the West and Southwest may be dry as the dessert that it is by mid-century, as the Colorado River and the vast reservoirs it supports dry up.

That's the conclusion of a new study to be published in Water Resources Research, which concludes that -- under present management conditions and population growth projections -- climate change could result in a 50-50 chance of bone-dry reservoirs on any given year. Considering that those 12 reservoirs currently hold about four years' worth of water, that's a shocking fact, even in the midst of a decade-long drought.

Reduction in mountain snowpack and spring runoff is one of the clearest consequences of global warming in the Continental U.S.: Shifting seasons and precipitation patterns, along with greater evaporation in high heat, is already leading to reduction in snowmelt. That results in greater wildfire risk and greater competition for scarcer water.

Some 30 million people rely on the Colorado directly for drinking water or farm irrigation -- and many more benefit from the massive diversions of water in the form of farm produce delivered to local grocery stores. But after 10 years of drought and rampant suburban sprawl the Colorado's reservoirs are at less than 60% of capacity.

The new study is actually more optimistic than one released in February 2008, published in the same journal, which predicted a 50% chance that Lake Mead and Lake Powell -- the two biggest reservoirs, which together account for more than 80% of the river's stored capacity -- would dry up by 2021. The new study sees only a 10% chance of that happening in any year through 2026.

By 2057, the chance rises to 25%, according to the new prediction. And that chance rises to 50% if climate change results in a 20% reduction in river flow.

But both studies come to the same conclusion: Management of water in the Colorado Basin has to change. The Colorado River has long been a subject of controversy, having been diverted, dammed and ditched to make the desert Southwest habitable. The Lake Mead/Lake Powell system includes the stretch of the Colorado River in northern Arizona. Aqueducts carry the water to Las Vegas, Los Angeles, San Diego and other communities in the Southwest.

"On average, drying caused by climate change would increase the risk of fully depleting reservoir storage by nearly ten times more than the risk we expect from population pressures alone," said Balaji Rajagopalan, author of the new study. "By mid-century this risk translates into a 50 percent chance in any given year of empty reservoirs, an enormous risk and huge water management challenge."

Whatever unfolds, the coming water crisis landed Las Vegas on The Daily Green's list of 10 Endangered Vacations. See what else made the list.

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