Slowly melting snowpack and filling reservoirs could improve drought in Boise. Here’s how
Despite much of Central and Southern Idaho being somewhere between a moderate to extreme drought, many of the region’s major water storage reservoirs and snowpack totals are well above their normal levels.
The snow water equivalent percentage — which measures how much liquid water is in the snow still on the ground — in the Boise Basin is at 127%, meaning there is 27% more liquid water in the snowpack than usual at this time of the year.
In some regions of Idaho, such as the Birch, Medicine Lodge, Beaver and Camas basins in East Idaho, the SWE percentage is as high as 1,614%.
So why is much of the state still considered to be in a drought?
The extreme numbers related to the SWE percentage can be misleading.
“The snowpack is gone or almost gone at most locations, and a small number divided by a really small number can produce a huge percentage of average values, even though there’s not much total snow out there,” said Timothy Link, professor of hydrology and director of the Water Resources Graduate Program at the University of Idaho, in an interview with the Idaho Statesman on Tuesday.
The Birch, Medicine Lodge, Beaver, and Camas basins have a high SWE percentage because 10.2 inches of SWE was measured at the Meadow Lake observation site. Typically only 0.7 inches is measured this time of the year, resulting in the incredibly high percentage.
The Boise Basin’s percentage is skewed because 7.2 inches was measured at Jackson Peak, 3,600% more than the 0.2 inches typically measured at this time of year.
Link said that most stations below 7,000 feet are recording no snow on the ground, and the stations that are high enough to record snow don’t cover an extensive area.
How reservoirs are helping Idaho
Although many SWE percentages are inflated, there are still some positives to the amount of snowpack left in the mountains.
“The delay in the snowpack (melting) is a huge help this year. Because what that does, it means we’re peaking now, as the irrigation season is really getting underway,” David Hoekema, hydrologist for the Idaho Department of Water Resources, told the Statesman.
As a result, what is not skewed is the amount of water in many of the Boise and Payette River Basin’s major storage reservoirs.
Many of the region’s major reservoirs are close to full because of the slow runoff from the melted snowpack. Arrowrock Reservoir east of Boise is 95% full, while Lake Cascade north of Boise is 92% full.
Water reservoirs are primarily used for irrigation, drinking water and water used in our homes daily.
“Instead of drafting the reservoirs right now, we’re filling them up and topping off,” Hoekema said. “So that puts us in a pretty good spot.”
Hoekema said that the snowpack statewide was approximately 70% of normal in 2022 and that the outlook earlier this year predicted a dry and challenging summer. But a more active weather pattern and cooler temperatures have produced good results for the reservoirs, so they’ll last longer into the summer.
Typically, such as in 2021, many of the state’s reservoirs are already being lowered by now. But with water still running into the reservoirs, it could help with short-term drought conditions this summer.
“I think there’s a pretty good chance, better than 50%, that water shortages on the Boise (River) will probably not occur, or they’ll be very minimal,” Hoekema said.
He was less optimistic about water shortage chances along the Snake River, especially on the eastern side of the state. By the end of the summer, Hoekema still expects the state to have “nothing left in the bank,” but he is optimistic for some short-term drought recovery.
Getting out of the drought
Nearly all of Idaho south of the Salmon River is in a moderate, severe or extreme drought, according to the National Integrated Drought Information System.
But Hoekema thinks that Southwest Idaho could see improved conditions this summer.
“In the short-term picture, I think we are seeing a pretty significant recovery from drought,” Hoekema said. “It just isn’t a recovery in the longer scale.”
Hoekema does not expect conditions in Idaho to be wholly solved this year. But with the summer outlook changed somewhat, at least the western part of the state could be on an upward trajectory.
“It will definitely not be the kind of record-setting shortages we were expecting on April 1, when we were looking at climatological normals,” Hoekema said. “It just looked like there wasn’t much hope of recovery. But the cool weather has really delayed that snow melt, and that’s the real story here.”