Low Spring Water Supplies Predicted

Although Arizona’s recent winter storms have raised snowpack levels, the state is still lagging behind the 30-year average by 30%.

“This winter’s low snowpacks pose a serious threat to the upcoming spring & summer runoff season, as well as for agriculture, & 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 & 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 Feb. 1st, Az 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 & 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 Jan. 15th.

Among the findings in the report, the statewide snowpack was measured at 71% of the 30-year average on Feb. 1st, compared with 44% on Jan. 15th. “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% of median on the Virgin River at Littlefield, to 86% of median on the Little Colorado River at Woodruff.

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

Among other findings reported by NRCS include combined Salt River Project (SRP) reservoir storage monitored at 61% of capacity with 1,409,495 acre-feet in storage on Feb. 1st, compared to 78% of capacity at this time a year ago. An acre foot of water equals 325,851 gallons & is enough to supply 2 families for a year. At San Carlos, Feb. 1st, reservoir storage was monitored at 31% of capacity with 272,500 acre-feet in storage, compared to 21% 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% of capacity on Feb. 1st. “Most areas in the Upper Colorado River basin currently have below average snowpacks as monitored Feb. 1st, by the snow surveyors,” Martinez said. “As a result, inflow to Lake Powell is now predicted at 74% 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% of average inflow forecast on Jan. 1st, when upper basin precipitation conditions were better,” Martinez added. Additionally, NRCS automated SNOTEL monitoring stations show the upper basin snowpack to be at 75% of the 30-year average on Feb. 1st.

For more info about snow surveys done by NRCS, go to az.nrcs.usda.gov/snow/.