California heads for a third dry year in a row

For those of us who don't rely on mountain snows as natural holding tanks for a large chunk of our water supply, it may seem odd to hear talk of drought when some ski resorts in the Sierras are talking 78 inches of packed powder.

The key is water content. A longstanding rule of thumb holds that 10 inches of snow holds an inch of water. But as anyone who has shoveled the stuff will tell you, there's snow (light and fluffy), and there's snow (wetter and heavier). Over at the CoCoRaHS blog (no, it's not a breakfast cereal), there's a tidy discussion of the range of snow-to-water values for the Rockies.

Suffice it to say that water managers are more interested in water-content numbers than in mere snow depth alone.

One long-term outlook

The picture for the region well into future isn't encouraging. A year ago, Tim Barnett and David Pierce, with the Scripps Institution of Oceanography, published a study saying that Lake Mead stands a 50-50 chance of running functionally dry by 2021 if water demand in the region the dam serves isn't reduced and if carbon dioxide emissions, and hence global warming, follow a business-as-usual path.

Functionally dry means the dam will still have some water in it, but the level will be too low to reach inlets that steer water to spillways or to turbines that run the dam's generators.

Even if you count yourself among the category of folks who shake their heads and roll their eyeballs at the concept of human-triggered global warming, studies of past climate regimes in the Southwest show the region is prone to very long-term droughts that would make the Dust Bowl look like a cool spell.

Maybe that's why John Wesley Powell, best known for his post-Civil War expedition through the Grand Canyon by boat, insisted so vehemently (without success) that the Southwest needed to be surveyed extensively before it was opened to settlers.

He was worried about the availability of water and the sustainability of development in the area. Some issues haven't changed.

In an upcoming post, we'll look at a tool scientists are using to help water managers figure out the most effective strategies for reducing one Southwestern city's demand for water.

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