May 25, 2007 Features & Images » Feature Story

Into Thin Air 

In the Western U.S., global warming has spawned a call for new dams – but there may not be any water to fill them

By Matt Jenkins

High Country News

The dream of the infinitely expanding West is getting beaten over the head with an empty bucket. Flows in the Colorado River, which is now entering its eighth straight year of drought, will be less than half of average this year. In the Sierra Nevada, snowpack is just 46 per cent of normal. And those numbers are likely to get even worse in the future, as droughts are amplified by global warming.

Now, water managers in the region are contemplating how to react, and new dams have been pitched as one possible response. In California, Gov. Arnold Schwarzenegger, R, announced on Jan. 9 that "with California's   booming population, and with the impact that global warming will cause to our snowpacks, we need more infrastructure." Just two days later, California state Sen. Dave Cogdill, R, picked up the battle standard and introduced a bill to raise $4 billion in bond money for two new dams, saying, "We have to act now."

Indeed, global warming is already changing the West's waterscape. Average temperatures in the region have increased by about 2 degrees Fahrenheit since the 1970s. A greater portion of each year's precipitation is falling as rain rather than snow, and snowpack — which serves as a natural, slow-release reservoir — is melting earlier than it used to; both changes are intensifying the pulse of winter and spring runoff.

Cogdill, who represents parts of the largely agricultural San Joaquin Valley, says that the continued loss of snowpack and the intensified bursts of seasonal runoff could exceed the storage capacity of California's existing dams. "If you don't do something about our ability to manage that water," he says, "more and more of it will run into the ocean, and late in the year we'll be in a real deficit."

New dams can catch excess bursts of water when they come out of the mountains, then spread those flows throughout the year. But it is becoming clearer that, for the West as a whole, more dams may not stem future water crises. New climate projections are hinting that in the future, the region won't just be warmer. It will also be drier.


Diminishing returns

Any effort to build more dams will be shadowed by the curse of diminishing returns. For one thing, there simply aren't many places left to put a dam, either in California or in the West as a whole. One of the two proposed California dams would be built at Temperance Flat, in the Sierra foothills near Fresno, to catch floodwater in the San Joaquin River. Yet possible dam sites are so limited that the dam would have to be built in an existing reservoir called Millerton Lake. The second, Sites Reservoir, would be built in the hills on the western edge of the Sacramento Valley, and would hold water from the Sacramento River.

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