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Mid-winter snow report predicts low spring water supplies

Feb 8, 2007 8:11 AM

Phoenix, February 6, 2007 – Although Arizona’s recent winter storms have raised snowpack levels, the state is still lagging behind the 30-year average by 30 percent.

“This winter’s low snowpacks pose a serious threat to the upcoming spring and summer runoff season, as well as for agriculture, and the natural resources of the state,” said Larry Martinez. Martinez is the water supply specialist for NRCS. “We are in need of more precipitation at this time and I am hoping this weather pattern breaks sometime soon to a more wet cycle for the remainder of the winter.”

The USDA’s Natural Resources Conservation Service (NRCS) has just released its February 1 Arizona Basin Outlook Report, which provides a seasonal water supply outlook for key watersheds in Arizona.

Contained in the report is snowpack data from Arizona’s 15 automated snow telemetry (SNOTEL) sites and 23 snow courses manually measured by a team of cooperative snow surveyors. The report shows that snowpack levels have risen substantially in the northern watersheds since the last report was issued on January 15.

Among the findings in the report, the statewide snowpack was measured at 71 percent of the 30-year average on February 1, compared with 44 percent on January 15. “All key watersheds are reporting below average snowpack levels at this time,” said Martinez. “If the current trend continues, this means less snowmelt runoff later in the season, especially for those streams that feed the reservoirs supplying water to central Arizona.”

Arizona’s long-range runoff forecasts closely mirror the states below-average snowpack readings. As a result, water users can expect well below median streamflow volumes through May. These volume forecasts range from 49 percent of median on the Virgin River at Littlefield, Arizona to 86 percent of median on the Little Colorado River at Woodruff, Arizona.

In the report, recent snow surveys show the snowpack in the Salt River Basin to have a snow water content measured at 86 percent of the 30-year average, while in the Verde River Basin, water content of the snowpack was measured at 69 percent of average. In the Little Colorado River Basin, water content of the snowpack was measured at 73 percent of average, while in the San Francisco-Upper Gila River Basin, snow water content of the snowpack was measured at 97 percent of average. Along the central Mogollon Rim, the snowpack was measured at 78 percent of average. At the Grand Canyon, snow surveys show the combined snowpack to have an extremely low water content monitored at 28 percent of average. On the Navajo Nation, the water content of the Chuska Mountains and Defiance Plateau snowpacks were measured by tribal surveyors at 56 and 75 percent of average, respectively. At the San Francisco Peaks, the snowpack was measured at 60 percent of average.

Among other findings reported by NRCS include combined Salt River Project (SRP) reservoir storage monitored at 61 percent of capacity with 1,409,495 acre-feet in storage on February 1, compared to 78

percent of capacity at this time a year ago. An acre foot of water equals 325,851 gallons and is enough to supply two families for a year. At San Carlos, February 1 reservoir storage was monitored at 31 percent of capacity with 272,500 acre-feet in storage, compared to 21 percent of capacity a year ago. “Incredibly, in-state reservoir storage levels remain in fair shape in spite of the on-going drought, thanks to the huge winter of 2005, which filled interior reservoirs to full capacity by springtime. The substantial runoff generated from the active summer monsoon of 2006 also benefited reservoir storage in recent months,” Martinez said. On the Colorado River, below average reservoir storage at Lake Powell continues to raise concern. At Lake Powell, reservoir storage stands at 11,703,000 acre-feet, or 48 percent of capacity on Feb. 1. “Most areas in the Upper Colorado River basin currently have below average snowpacks as monitored February 1 by the snow surveyors,” Martinez said. “As a result, inflow to Lake Powell is now predicted at 74 percent of the 30-year average (5,900,000 acre-feet) for the forecast period April-July, the time of year when greatest runoff normally occurs each season on the river. This is compared to 91 percent of average inflow forecast on January 1 when upper basin precipitation conditions were better,” Martinez added. Additionally, NRCS automated SNOTEL monitoring stations show the upper basin snowpack to be at 75 percent of the 30-year average on February 1. For more information about snow surveys done by NRCS, go to http://www.az.nrcs.usda.gov/snow/.

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