Spring and summer water supply estimates fell for most of the West, according to data from the third 2016 forecast by USDA’s Natural Resources Conservation Service. Gains from record early-season snowfall are largely declining due to changing weather conditions.
“December snows got us off to a strong start,” NRCS Hydrologist Cara McCarthy said. “But snowpack increases stalled in recent weeks throughout much of the West due to warm temperatures combined with lower precipitation.”
Streamflow forecasts in some areas have seen a double-digit reduction. “The most dramatic decrease is in the Southwest,” said McCarthy. “The streamflow forecast for the upper Colorado River basin fell by 20 percent since last month.” The downriver states of Nevada, Arizona, and California depend on the Colorado River water supply.
“Even with recent stagnant snowpack growth, snow in many drought-affected areas is more robust this year,” McCarthy said. “In Oregon, Washington, Nevada and parts of California, 2015’s record-low areas are now showing near-normal.”
This is the third forecast of the season. Subsequent forecasts will increase in accuracy as potential is realized. “We’re nearing the end of snow accumulation season, but changes could still be ahead for the upcoming spring and summer water supply,” McCarthy said.
In Western states where snowmelt accounts for the majority of seasonal water supply, information about snowpack serves as an indicator of future water availability. Streamflow in the West consists largely of accumulated mountain snow that melts and flows into streams as temperatures warm in spring and summer. NRCS scientists analyze the snowpack, precipitation, air temperature and other measurements taken from remote sites to develop the water supply forecasts.
NRCS monitors conditions year-round and will continue to issue monthly forecasts until May. The water supply forecast is part of several USDA efforts to improve public awareness and manage the impacts of climate change, including drought and other extreme weather events.
Water supply forecasts inform decisions made by individual producers and irrigation districts at the local level; as well dam operators, water managers and federal partners at the regional and national levels. State level information is available for the twelve states monitored on the NRCS State Water Supply Outlook webpage.