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Megadrought across the West worst since at least 800 AD

Researchers at UCLA say even without climate change, it still would have been dry, but human impacts are what made the last 22 years the driest period on record

Yamcolo Reservoir, seen here Sept. 24, sits at about 9,500 feet of elevation in the Flat Tops Mountains. All the water it contains designated for agricultural use in the last two years has been used and it likely won't fill this year, meaning some users won't get the water they need.
Dylan Anderson/Steamboat Pilot & Today

Warmer temperatures are drying out soils and vegetation across the West so much that the last 22 years are now collectively the driest since at least 800 A.D., according to a new study led by the University of California Los Angeles.

Scientists and policymakers have repeatedly stressed global warming needs to be limited to 1.5 degrees Celsius above preindustrial averages to avoid catastrophic climate outcomes. The West has warmed by more than half that since 2000.

The study, published Monday, Feb. 14, in the journal Nature Climate Change, looked at climate patterns from Southern Montana to Northern Mexico, and from the Rocky Mountains to the Pacific Ocean. The study found the average temperature across much of the West has increased by .91 degrees Celsius (about 1.64 Fahrenheit) since 2000.



Recent trends — particularly high temperatures and low precipitation from summer 2020 through summer 2021 — are what pushed the beginning of the millennium into the top spot when it comes to drought, the study found.

This period likely would have been dry anyway, but the impacts of human-caused climate change are what made it the worst on record, the study concludes, with humans responsible for 42% of the soil moisture deficit seen since 2000.



While drought has been the norm on the Western Slope for decades, the study highlights how different this megadrought — defined by a drought lasting longer than 20 years — is compared to other periods that tree ring data has identified as particularly dry times.

“Without climate change, the past 22 years would have probably still been the driest period in 300 years,” said Park Williams, a UCLA geographer and lead author on the study. “But it wouldn’t be holding a candle to megadroughts in the 1500s, 1200s or 1100s.”

Doug Monger, Routt County’s representative on the board of the Colorado River District, said 2021 was one of the worst years for water.

“2022 is mirroring it totally,” Monger said.

The Yampa River Basin is following the same trend of the entire Colorado River Basin, Monger said, where the amount of water snow represents is falling below the 30-year-average, and the amount that actually makes it into the river is just a fraction of that.

“Runoff ended up being 32% (of average),” Monger said, referring to last spring. “That’s how short we are.”

Monger noted that the averages are changing as well, and Andy Mueller, general manager of the Colorado River District, said comparisons based on today’s average can be quite a bit different than previous ones.

“We are currently expecting a 78% runoff into Lake Powell under the new 30-year-average,” Mueller said. “If the prior 30-year average was still in place, that 78% would be closer to 68%.”

The study notes one wet year is highly unlikely to get the region out of drought conditions, and Mueller said he isn’t aware of anyone studying climate change who expects any relief in the foreseeable future.

The snowpack so far this year is lagging behind the average and stands at almost the same level it was at this time last year. Still, Andy Rossi, general manager of the Upper Yampa Water Conservancy District, said he believes they will have a reasonable ability to fill Stagecoach Reservoir.

“That can paint somewhat of a not-too-bad picture,” Rossi said. “But what that translates to on the ground for a water user can be much more severe because they don’t have access to those kinds of resources.”

Every drop of water meant for agricultural use in Yamcolo Reservoir has been used the last two years, Rossi said, and he doesn’t expect to be able to fill the reservoir this year. Because each drop is already spoken for, “if we don’t fill it, somebody’s not getting their water,” Rossi said.

Farther down stream, drought has Lake Powell and Lake Mead — the two main reservoirs on the Colorado River — at their lowest levels ever. Mueller said another concern is these reservoirs could drop so low they can no longer generate power, which many Western power cooperatives rely on.

Mueller said water is being released from other reservoirs and being held in Lake Powell to ensure power production can continue, but that is just a temporary solution to a much larger problem.

“You can empty one bucket to fill another, but there’s nothing to fill either of those buckets once they’re gone,” Mueller said.


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