The new year is bringing welcome news for Idaho water users, with fall precipitation and winter snowstorms bringing relief from drought.
Although Idaho is not out of the woods yet, drought severity has been reduced across most regions of the state, according to the January Water Supply Outlook Report released by the Natural Resources Conservation Service in Idaho.
“Improvements in soil moisture and shallow groundwater conditions throughout the fall along with above-normal December snowfall provide optimism for more efficient runoff come early spring,” the report said.
After some early season snowfall in October, snowpack remained alarmingly low until mid-December, when winter storms and low temperatures finally arrived. The second half of December brought significant increases in snow water equivalent across the state.
Snowpack is above normal in all basins north of the Snake River Plain and near normal in most Southern Snake basins.
“We have some concerns about SWE (snow water equivalent) totals in the Bruneau, Salmon Falls and Goose Creak (Oakley) basins, where snowpack totals are slightly below normal,” NRCS said.
These basins generally reach their snowpack peak and subsequent snowmelt runoff earlier in the season than much of the rest of Idaho, so there’s less time to catch up than in other areas.
“At this time, our primary concern for meeting irrigation demand this growing season is the low reservoir carryover storage that kicked off water year 2022,” said Corey Loveland, supervisory hydrologist for NRCS Snow Survey in Idaho.
“Carryover storage was well below normal in all major reservoir systems across the region. Although reservoir storage continues to increase, we will need an above-average snowpack to fill reservoirs this spring,” he said.
As of Jan. 1, reservoirs in both the Upper Snake River Basin and the Boise River Basin were at 36% of capacity, according to the Bureau of Reclamation.
Jan. 1 streamflow forecasts, where available, generally reflect the current mountain snowpack and precipitation conditions. That’s showing near-normal expected streamflow volumes for April through July and April through September in much of the Upper Snake Basin, NRCS said.
Likewise, normal to much-above-normal streamflow volumes are forecast for the Owyhee and Bear River basins.
“These early season forecasts should be approached with a degree of caution, as we still have multiple months of unknown winter weather in front of us — which will directly impact future streamflow forecasts and eventually spring and summer runoff,” NRCS said.
The National Oceanic and Atmospheric Administration’s one-month outlook suggests increased odds of above-normal precipitation and lower-than-average temperatures across most of Idaho. These typical La Nina conditions generally favor northern and central Idaho for the remaining winter months.
NOAA’s three-month outlook predicts equal chances for warm, neutral or cooler conditions in the Southern Snake River and Snake headwater basins.
Idaho needs 135% to 195% of normal precipitation to completely end drought conditions by April 1, so the probability of improving drought conditions is much higher than the probability of ending them, NRCS said.