Storms in the first dozen days of February boosted the previously lagging snowpack to a point that southern Idaho irrigators can expect adequate water supplies this year if the rest of winter unfolds as forecasters predict.
“Things are looking good, but we still need more precipitation,” USDA Natural Resources Conservation Service Water Supply Specialist Ron Abramovich said at a Feb. 13 meeting of the Idaho Water Supply Committee in Boise.
Regional snowpack remains well behind the unusually high levels seen two years ago but has improved considerably since 2019 began. NRCS data as of Feb. 13 show snowpack at more than 90 percent of the long-term average in many Idaho river basins, including some at 100-plus percent.
In the Boise River Basin, 80 percent of long-term average precipitation for the entire month of February had arrived by Feb. 12, Abramovich said, prompting more optimistic forecasts.
He said the Boise Basin needs 64 percent of average April-through-September runoff for irrigation supplies to be adequate this year. That’s an improvement from Feb. 1, when forecasters thought irrigators in the basin would need runoff to be 67 percent of average.
Recent snow at higher elevations, and mixed rain and snow lower, brightened this year’s streamflow forecast for the Boise Basin. Runoff, and thus streamflow, is now projected at 80 percent of the long-term average this year, a 13-percentage point gain from Feb. 1. The situation could change by April, but the rest of February looks good for snowpack given expected wet, cold conditions, Abramovich said.
Ryan Hedrick, hydrologist at the U.S. Bureau of Reclamation Middle Snake Field Office in Boise, said strong precipitation in early February helped ease earlier concerns that Boise-area reservoirs would not fill. But more will be needed in the next two months to ensure adequate supplies.
“We’ve just got to wait and see,” he said.
In south-central and eastern Idaho, and parts of Wyoming, reservoir levels are at 132 percent of average for this time of year, said civil engineer Brian Stevens at the Bureau of Reclamation Upper Snake Field office in Heyburn, Idaho. Substantial water was carried over from 2018, and the reservoirs see good winter inflows.
When reservoirs are filling ahead of schedule, the potential for additional aquifer-recharge projects increases in the Snake River Watershed above Milner Dam in south central Idaho, he said.
Much of the West has significantly more snowpack compared to a year ago, said Troy Lindquist, National Weather Service senior hydrologist in Boise. Examples include the Oregon stretch of the Cascade Range, the Sierra Nevada, the Four Corners region and Idaho.
Adequate water supplies and some drought relief could materialize if the trend holds, he said. But forecasts favor above-normal spring and summer temperatures in the West, historically associated with snow melting earlier, plants and farmers needing more water, and consumers using more hydroelectric power to run air conditioners.