Drying Up

Thanks to drought and warm weather, snowpack through much of the West is taking a big hit, reducing streamflow forecasts for spring and summer.

By Tom Yulsman

As of March 15, 2012, in the Upper Colorado River Basin snowpack was just 72 percent of average, according to data from the Natural Resources Conservation Service. (via ftp)

A winter of seemingly relentless wind has given way to balmy and mercifully calm weather, bringing daffodils and sunnier spirits — but also heralding a potentially dry and vexing season ahead for much of the West.

Already, large portions of California, Nevada, Arizona and New Mexico are experiencing drought conditions rated as severe to exceptional. And abnormally dry conditions as well as some significant areas of drought extend across Utah and Colorado too. So it should be no surprise that mountain snowpack is running well below average through much of the West — marking a dramatic turn-around from bountiful conditions at about this time last year.

Mountain snowpack in the Upper Colorado River Basin is running well below average for this time of year — and it seems to have stopped accumulating just at a time when it should be heading toward a peak. Much of the water that ultimately helps replenish Lake Powell and Lake Mead originates as runoff in the basin. (Graph: National Resources Conservation Service). (via ftp)

In the Upper Colorado River Basin, for example, snowpack was just 72 percent of average as of March 15 — and dropping steadily. Statewide, the figure is only a few percentage points better. But we’re relatively lucky compared to California and Nevada. In a map from the Natural Resources Conservation Service, the Sierra Nevada Range is colored fire-engine red — indicative of snowpack that is as low as 25 percent of average.

Throughout much of the West, the water content of snowpack — a good predictor of the amount of runoff that will be available to cities and farms throughout the region — typically peaks between the end of March and mid-April. So there’s not much time left to make up the deficit.

Drought and the resulting thin snowpack are conspiring to reduce streamflows throughout much of the West this spring and summer, according to the Natural Resources Conservation Service (via www.wcc.nrcs.usda.gov)

La Niña, the climatic phenomenon that can contribute to drier than average conditions in the Southwest in particular, has begun to ease, and according to the Climate Prediction Center, it should be gone by the end of April. But like the faint odor of smoke that lingers after a fire, La Niña’s influence is expected to continue through at least late spring. That means higher than average chances for dry conditions from Southern California northeastward into Colorado and out onto the Central Plans. (South Texas, the Gulf Coast and the Southern Atlantic states also face enhanced chances for dry conditions through this period.)

All of this does not bode well for runoff in the Colorado River Basin, whose waterways serve the needs of nearly 30 million people in seven states and Mexico, and irrigate more than three million acres of crops and pasture. In fact, below average stream flows are forecast for the Colorado Basin, as well as in California, Nevada, Arizona and parts of New Mexico.

Prior to last year, 11 years of drought in the Colorado River Basin had caused water levels in Lake Powell and Lake Mead, the two giant reservoirs on the mainstem of the Colorado River, to drop steadily. On Oct. 17, 2010, Mead dropped to a record low level — one not seen since the reservoir began to fill in the 1930s.

Last year’s bountiful snowpack and resulting rip-roaring streamflows raised hopes that the situation might ease. And there have been upticks in the level of water in the reservoirs, which serve as the hydrologic equivalent of savings banks to see the region through dry times. But both are still well below capacity. Powell is at about 63 percent of capacity, whereas Mead is at just 57 percent. And the U.S. Bureau of Reclamation is forecasting that between April and July, the amount of water flowing in the Colorado River will be only 74 percent of average.

So unless conditions turn around rapidly and dramatically — an unlikely scenario — it looks like we’ll be drawing down those savings accounts again.

Update, 3/16:  No sooner had we posted this story on drought and dwindling snowpack than the National Weather Service issued a forecast for California’s Sierra Nevada Range calling for 1 to 4 feet of snow above 6,000 feet, today through Saturday afternoon. Currently, much of the Sierra Nevada’s snowpack is between 25 and 49 percent of average. How much will this storm help? Check back for another update to find out.