Wednesday, April 17, 2013

Short snowpack raises water concerns

Dry winter could limit supplies for agriculture

Express Staff Writer

Snowpack levels across the state vary widely. The Idaho Department of Water Resources reported recently that the snowpack in the Big Wood River basin is far below average and could potentially cause agricultural water shortages. Courtesy graphic

    A dry beginning of the year put a dent in the Idaho snowpack and could result in agricultural water shortages, states a report released by the Natural Resources Conservation Service.
    The NRCS released a report on April 1 documenting poor precipitation statewide and forecasting low stream flows in much of the state. The report states that a dry March followed a dry January and February, putting a large dent in the above-average snowpack set up by above-average early-season snow.
    “Instead of maintaining snow levels from month to month if near normal precipitation amounts would have fallen, snow percentages decreased again,” the report states. “The bad news is the combined impacts of three months of below normal precipitation. January, February and March combined precipitation this year was [a] record low for 16 [monitoring] sites from the Payette Basin to Little Lost Basin.”
    The report says that the water year this year—which started on April 1—is expected to be similar to 2002, which was a drought year through much of the West.
    The Idaho Department of Water Resources said on April 1 that the Big Wood River basin snowpack stood at 68 percent of average.
    The NRCS and IDWR have recently changed the “normal” statistics used to compare snowpacks, however. Instead of being compared against an average figure from snow years 1971-2000, snowpacks are measured against a median snowpack figure from 1981 to 2010. A report from the NRCS states that as the decade between 2000 and 2010 was relatively drier than previous decades, the new “normal” snowpack and streamflow amounts have declined.
    IDWR reports that the snowpack in the Big Wood River basin is at 79 percent of the new normal median. That number puts it on par with much of the state, such as the Salmon River basin, the Payette basin and the Little Wood basin, which stands at 85 percent of the median.
    The report says that March precipitation was at 50 percent of average in the Big Wood and Lost River basins.
    Water reserves in Magic Reservoir will likely suffer from the poor precipitation. New water added to the  reservoir south of Bellevue is only expected to reach 63 percent of average this year, with 167,000 acre-feet from the snowpack runoff. Adding that figure to Magic Reservoir’s current storage, the reservoir is expected to have 208,000 acre-feet available this year.
    “[That figure] is short of the 275,000 acre-feet needed for an adequate surface water supply,” the report states. “[The reservoir] will not fill and may only provide an irrigation season of about 45 days.”
    Little Wood Reservoir and the Mackay Reservoir are expected to fare better. The Little Wood Reservoir is already 83 percent full, and the report states that it should provide an adequate water supply. Shortages are possible from the Mackay Reservoir, but the report states that it is already 83 percent full and that moisture from last year should help sustain flows through this year.
    As for whether spring rains will help streamflows, the NRCS remains doubtful. This year seems similar to 2002, the report states, and “April and May 2002 precipitation was nothing to brag about with below to near average amounts across the state.”

Kate Wutz:

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