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    NASA Snow-Mapping Project May Help Calif. Forecast Water Supply

    By By Stephanie Paige Ogburn, E&E reporter
    December 10, 2013, 8:26:52 AM EST

    SAN FRANCISCO -- A new NASA research effort has the potential to shift how scientists and water managers gauge winter snowpack and manage water in the West.

    Millions of people in the western United States depend on winter snowfall for the water they use year-round.

    Yet water managers in charge of storing and distributing this water must often rely on imperfect estimates of how much water is available each year, because accurate measures of water runoff from snowpack are difficult to create.

    "We don't really know the mountain snowpack well at all," said Thomas Painter, a researcher at NASA's Jet Propulsion Laboratory who presented his research yesterday at the American Geophysical Union conference in San Francisco.

    Last year, Painter and his partners pioneered the Airborne Snow Observatory.

    The goal of the project is to transform scientists' understanding of snow and water availability by helping them accurately measure that snowpack and the speed at which the snow will melt.

    The project uses Lidar technology to create highly accurate measurements of snow depth while also making measurements of snow reflectivity, or albedo, to estimate how quickly the snow will melt. The instruments are carried in a Twin Otter plane, which flies back and forth over a snow-covered basin, creating a map of snow depth.


    Seeing through the snow

    All these data are compressed into a map of snowpack that is far more accurate than any other estimation of snow depth in the mountains.

    "You can start seeing that detail in a way that was never before possible," said Jessica Lundquist, a hydrologist at the University of Washington who is participating in the research.

    In the first year of the project, the research was able to significantly improve on the forecast for the amount of water that would flow into Hetch Hetchy reservoir, which supplies water to 2.6 million people in the San Francisco Bay Area.

    As mountain snow melts off in the spring from April to June, the reservoir slowly fills.

    Water managers want that to happen, but if they let it fill too early, they risk uncontrolled overflows. This essentially wastes the water, and the rush of an overflow can also hurt the ecosystem below.

    On the other hand, if managers spill too much water out in anticipation of late-spring snowmelt coming down from the mountains and then the water fails to come, they risk underfilling the reservoir. Later in the season, this could mean the reservoir has too little water when it is needed the most.

    The information from Painter's project improves the water runoff forecast by providing a very accurate picture of how much snow is in the mountains and how quickly it is melting.

    Last season, forecasts based on models run without the data from the Airborne Snow Observatory overpredicted the amount of water that would flow into Hetch Hetchy by 32,000 acre-feet of water. (An acre-foot is the amount of water it takes to cover an acre of land 1 foot deep).

    Climate change may increase the need

    If dam managers were relying on those models alone, they would have released too much water from the dam too early. This sort of information could be very valuable for water managers, but it is also an expensive effort.

    Painter's plan is to prove that the benefits are worth the cost, which was about $1.4 million for the season last year, just measuring one basin in the Sierra Nevada mountain range.

    NASA is partnering for three years with the California Department of Water Resources to fund the project, which will help the agency and its partners see how well the investment pays off. This year the team will focus again on the Tuolumne River Basin, which feeds Hetch Hetchy.

    Eventually, Painter wants to cover all of the Sierra Nevada. Then he hopes to expand to the Colorado River Basin, where he is already doing some observing work, and beyond.

    "At some point in the next few years, we're looking toward that transition into a Westwide capability," Painter said. The data collected by the project may become more valuable in the future, as climate change alters the patterns of winter storms and speeds up snowmelt, he noted.

    In the future, NASA hopes to use this research to improve how it monitors snowpack from space, perhaps launching satellites that can do what Painter is now doing with aircraft monitoring, said Bradley Doorn, a manager in the water resources program at NASA headquarters.

    "In the West, understanding the water resources is critically important," he added.

    Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.

    E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.

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