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How much water in that snowpack? Scientists seek a better gauge.

More accurate, more frequent measurements of mountain snowpacks will allow water managers to mete out reservoirs with greater confidence. Two watersheds in the western US are testing grounds for a new aerial approach.

By Staff writer / May 4, 2013

A snow course marker, used for the Department of Water Resources snow survey, is seen against the dwindling Sierra Nevada snow pack at the Phillips Station near Echo Summit Calif., May 2. Frank Gehrke, chief of snow surveys for the Department of Water Resources, found no snow at the Phillips Station snow course, which he said is not unusual for May.

Rich Pedroncelli/AP


Scientists are testing a new approach for gauging the amount of water stored in mountain snows – reservoirs that supply more than 75 percent of the fresh water in the western US and that slake the thirst of some 1.5 billion people around the globe.

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The aim is to measure the snow's water content more accurately and more frequently, so that water managers can mete out water stored in reservoirs more effectively. The data also are expected to improve snowmelt forecasts as a melt season progresses.

The three-year demonstration project is focusing on a watershed in California's southern Sierra Nevada Mountains that provides San Francisco with water and another watershed in Colorado that feeds the Upper Colorado River Basin.

Rapid population growth and the subsequent demand on water resources in a drought-prone region are enough to justify the effort, suggests Thomas Painter, a researcher at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the lead scientist on the project. Dr. Painter's research focuses on Earth's water and carbon cycles.

But the issue becomes more critical in the face of global warming. Taken as a whole, the West's mountains have experienced a decline in April snowpack since the 1950s, studies indicate, although some portions of the West's mountain ranges, such as the southern Sierras, have seen increases in April snowpack.

For the northern Rockies, the decline is one of the most severe seen at any time in the past 1,000 years, according to a study published in 2011. The research team attributed the trend to natural climate swings superimposed on a long-term warming trend triggered by a buildup of greenhouse gases in the atmosphere from burning fossil fuels and from land-use changes.

"In the western US, we've built ourselves around this very nice synchronicity between the mountain snowpack and human-made reservoirs," Dr. Painter says, referring to the complementary role each plays in meeting the region's water needs. At the start of a water year, the reservoirs hold what's left of last year's snowmelt. The snowpack serves as a natural reservoir that releases its supply gradually, topping off human-built reservoirs at a pace that in principle keeps water available for use during the summer and into fall.


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