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It's getting warmer in here - and drier

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denvern | Jul 23, 2010 12:00 PM

A new report from the Natural Resources Defense Council (NRDC) offers a mixed picture of how climate change will affect Western water supplies. Some places will see more moisture, most will see less. For the majority of the region, sustainability of water resources is set to become a serious problem.

The study was conducted by the consulting firm Tetra Tech, which, according to its website, has at different times been contracted by the Navy, the Air Force and the Environmental Protection Agency, among other clients – suffice to say I have a fair amount of confidence in their methodology.

Comparing the period from 1961 - 1990 with 2020 - 2039, Tetra Tech’s study projects great swaths of the West will see a decrease in precipitation. Note the particularly troublesome spots in Arizona, New Mexico and California, all of which will see more than a one-inch decrease in precipitation per year. (Also note the area around Puget Sound - yeah, Seattle's just going to get even wetter).

West precipitation 2020

 

This second map begins to tell the real story, and for much of the West the picture starts getting pretty bleak. This map compares the total freshwater withdrawal (the amount of freshwater that will be used by inhabitants, taking into account population growth estimates) and the total available precipitation (the amount of water available after natural evaporation and water usage by plants). Counties in bright red will be using between 100 and 500 percent of their available freshwater: use your high level math to calculate how sustainable that is (or just look at the fourth map, below). Counties in deep red are even worse off.

Freshwater v Water Usage

Finally, check out the study's concluding maps. Making calculations based on the projected available precipitation, existing water storage, dependence on groundwater reserves, susceptibility to drought, projected increases in water use, and more, the study's authors determined how unsustainable the water supply is in counties across the United States. The first Water Supply Sustainability Index map assumes no climate change takes place. Even without climate change, parts of California, Nevada and Arizona are seriously threatened, and much of the West isn't in a lot better shape.

Water no climate change

For the second index map, the climate change variable is added into the calculus. The result is dramatic, and alarming.

Water with climate change

The Ogallala Aquifer-dependent plains look to be in serious trouble, as do parts of New Mexico and Utah, nearly all of Arizona, and all population centers in California and Nevada.

You may want to start planning ahead for a much drier West, unless you, like Senator Inhofe, believe climate change is the greatest hoax ever perpetrated on the American people (a dubious claim on its face for those who remember the Taco Liberty Bell and the flying penguins).

Denver Nicks is a High Country News intern.

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