‘Really tight water year’: Drought, low snowpack may foretell Idaho’s climate future

BOISE (Idaho Statesman) — Much of Southern Idaho, cut through in scythe-like fashion by the Snake River Plain, relies on the frozen water stored in the state’s mountains to fill its rivers. When winter ends and summer’s broiling heat arrives, it is these snowy peaks that serve as the state’s reservoir, filling the Salmon, Snake, Big Lost, Boise and other tributaries with cold, clear water.

But as the amount of snowfall declines, with scientists citing the effects of climate change as a key contributor, major problems arise for the state’s ecosystems, residents and agriculture industry.

And that erosion is already underway.

By the turn of the century, Idaho could see reductions of 35%-65% of its snowpack, according to a study published in Nature Reviews Earth & Environment last year.

After a dry winter in 2019-20, researchers were hoping for a turnaround. But last winter, Idaho had only 87% of its normal snowpack, and that was a bad combination when combined with the second-worst spring drought on record, said David Hoekema, a hydrologist at the Idaho Department of Water Resources.

Making matters worse was that dry soil absorbed much of that below-average snowpack, leading to only 53% of normal runoff, Hoekema said.

Idaho’s dry weather in 2021 saw over two-thirds of the state in extreme or exceptional drought — the two highest categories — in early October. This month, most areas of the state are listed in moderate to severe drought, according to the U.S. Drought Monitor.

As such, a wetter winter was sorely needed to fill up the state’s streams and reservoirs, but since a spell of storms in late December and early January, much of the state has seen weeks with little to no snowfall or precipitation.

A ridge of high pressure along the Pacific Coast blocked storms for the past month, and the rest of February is likely to remain dry, Hoekema said.

With Idaho’s mountains in need of more snow to reach what is considered “normal” snowpack levels, Hoekema said he is “very concerned” the drought will intensify this year, he said in an email, which could affect agriculture, landscapes and residents this summer just as it did last year, when irrigation water that normally runs till October had to be cut off early.

“If that materializes, it’ll lead us into a really tight water year,” Hoekema said.

And those are becoming more frequent.

Between the 1940s and the mid-2010s, streams throughout the state saw an average flow reduction of 20%, according to Charlie Luce, a research hydrologist at the Rocky Mountain Research Station, which is part of the U.S. Forest Service. And during the driest years, streams saw reductions of up to 40%.

Luce said the changes are associated with shifts in weather patterns consistent with expectations of climate change in the Pacific Northwest region, which have led to reduced precipitation in the high mountains.

With an increase in average temperatures, Luce described the lower precipitation in dry years and the larger portion of precipitation falling as rain rather than snow as a “one-two punch” that can further restrict the state’s water supply. Luce said he projects there will be more years with low soil moisture, which also decreases runoff into streams and reservoirs.

OUTLOOK IN IDAHO AFTER A DRY SPELL

The amount of snowfall in a given winter is not the only factor that determines how full Idaho’s reservoirs get. Soil moisture levels are also important, as well as weather patterns that come in the spring and can help flush snow down from the mountains.

In the southern part of the state, last year’s skimpy precipitation left reservoir systems close to dry, meaning only a wetter-than-average winter this year would allow water managers to rest easy.

The 2020-21 winter was a La Nina year — an atmospheric phenomenon that generally brings more precipitation to the Northern Rockies. This winter is also a La Nina period, and trends over the past 40 years indicate that back-to-back La Ninas get subsequently drier, Hoekema said, which does not bode well for runoff.

Hoekema said the Boise River system may be able to “slide through” with 75% of normal runoff this year, but that figure would leave the system dry come next fall. In the Snake River system, the situation is more dire, as the system likely needs 120% of normal snowpack to get through the summer.

In the middle of February, the state’s snow-water equivalent, a measure of how much water is contained in snow, was lower in many places than what Hoekema predicts is needed, with portions of Southern Idaho seeing figures as low as 70% of normal. The situation is better in the Little Wood and Big Lost basins of Central Idaho, where the levels are 107% and 108% of normal, respectively, according to data from the Natural Resources Conservation Service.

Hoekema wrote in an email that late-winter snows could greatly improve the situation, but “the window for recovery is closing fast.”

In the Snake River system, the likelihood of the reservoir filling up for the year “seems pretty dismal at this point,” Hoekema said.

The upper Snake, in East Idaho, would need an additional 8.5 inches of snow to reach normal conditions. Since Jan. 9, the particular area in need has seen only half an inch of accumulation, Hoekema said.

In the Boise system, the situation is a little less clear, he said.

The system would start March with 87% of normal snowpack if it received just another inch of snow in the next few weeks. “At this point, it is really difficult to predict whether or not the Boise basin will see drought intensify,” Hoekema said. “It all depends on what happens in March.”

AGRICULTURE: ‘SOME OF THE WORST YIELDS … IN THE NEXT 100 YEARS’

Drought connected to climate change is expected to affect Idaho’s farming economy significantly, according to a recent report from the University of Idaho.

The report, called the Idaho Climate-Economy Impacts Assessment, found that though crop yields for plants in Idaho appear to have risen over the past 60 years, the volatility among rain-fed crops is more than among irrigated crops.

Last year in North Idaho, where agriculture is largely rain-fed, farmers experienced “some of the worst yields we’ll probably see in the next 100 years,” Hoekema said.

Chickpeas, which are largely grown in the north, saw yields down 50% across the state, and grain yields were down 20%, with the biggest losses in the north.

“There were whole farms where they just weren’t able to harvest anything and had a complete loss of their grain,” he said.

In the coming decades, the effect on agriculture is expected to be more severe. The University of Idaho report found that the number of days with temperatures of at least 100 degrees would increase significantly by 2040.

From 1971 to 2000, 6.9% of the land area of Idaho experienced one or more days with these scorching temperatures, also known as “heat stress” days. If the use of greenhouse gas emissions continues unabated, 61.8% of Idaho is expected to experience one or more such days between 2040 and 2069, while 18.5% will face 10 or more extremely hot days and 5.4% will see 25 or more, the report said.

The effect is predicted to be especially bad in the central and western portions of the state.

THE OWYHEES: A CLIMATE INDICATOR

As temperatures rise in Idaho, Hoekema said one place to look for faster, more appreciable indications of climate change is in the Owyhee Mountains, which cut diagonally across Southwest Idaho.

In the mountains of Central Idaho, many peaks are over 10,000 feet tall, which brings average temperatures well below freezing during the winter, according to data from the Western Regional Climate Center.

But the Owhyees, while still mountainous, are at lower elevation, with peaks around 8,000 feet. The difference makes the range a warmer environment, with winter temperatures that hover around freezing.

“Minimum winter temperatures are not going as low as they used to be,” Hoekema said. “If nighttime temperatures go below freezing, it slows runoff. But if temperatures are higher, it makes it harder to keep the snowpack in the mountains without melting.”

Between 1939 and 1987, the Owyhee Basin, which covers the southwestern corner of the Gem State and stretches northwest into Oregon and southeast into Nevada, experienced one multiyear drought: 1960 to 1962. A single-year drought seared the region in 1955.

But since 1987, the basin has been hit by three multiyear droughts — 1991-1992, 2001-2004 and 2013-2016 — and one single-year drought, in 1988, Hoekema said.

Hoekema said he is currently studying the region, trying to understand whether the increase in drought is caused by warming temperatures or less precipitation.

“If you see a climate signal in Idaho, it will be first in the Owyhees,” he said.

CLIMATE TRENDS: ‘OPPORTUNITIES TO LIMIT THE NEGATIVE IMPACT’

If the burning of greenhouse gases continues without major reductions, researchers predict there could be years of low or even no snow in the mountains of the Western U.S. in the coming decades.

The Nature study, published in November, synthesized climate models from other peer-reviewed studies to come up with a set of projections for what the future holds, and the potentials are stark: By 2100, Western mountains could see declines of between around 40% and 65% in snowfall.

Between 2050 and 2100, 78%-94% of years could see little to no snowpack, according to the analysis.

The synthesis in Nature did not specifically examine Idaho’s mountains, but Ben Hatchett, a co-author and assistant research professor at the Western Regional Climate Center, said Idaho’s peaks likely would see similar reductions in snowpack by the end of the century.

In fact, ranges in the Gem State could see larger reductions than Colorado’s Rocky Mountains because of Idaho’s comparatively lower elevations, he said.

Hatchett said Idaho’s mountains likely will be more resilient than some other ranges in the West — such as the Cascades or Sierra Nevadas — because of their characteristically colder temperatures, but major declines are still projected.

“The amount of decline will really strongly depend on how much warming actually occurs at the regional scale throughout the whole western part of North America,” he said.

Since 1975, temperatures in Idaho have risen about 0.24 degrees Celsius per decade, meaning that air temperature increases in the state have matched or surpassed the global average of a little more than 1 degree Celsius since the late 19th century, according to the report.

Though various climate models have different predictions, they all cannot account for the already documented increases in global temperatures without including human-caused greenhouse gas emissions, Hatchett said.

“If you don’t put in the anthropogenic greenhouse gas emissions, you don’t simulate an Earth that is as warm as it is today,” he said.

Rather than being a harbinger of doom and gloom, Hatchett said he hopes to motivate Western states to make the necessary changes to halt the worst effects of climate change.

“Even though the predictions are pretty dire, we don’t want to forget that we still have a lot of opportunities to limit the negative impact,” he said. And if Western states prepare for the worst and the worst doesn’t happen, “we’re still going to be a lot better off.”

Hatchett said part of the response to this problem will require some “pretty fundamental changes” to how water is used. He said solutions to the problem need to provide opportunities for different economic sectors to continue to succeed.

“How can we make this so that everyone can win more often?” he said. “We need everyone at the table, ready to bargain.”