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It's been a good year for Colorado River snowmelt. But dry soil, high temperatures could erase gains

High in the Rocky Mountains, spring is the time of year when altitude makes all the difference. Above the treeline, the mountains have been rendered almost featureless, blanketed by the deepest snow they’ll see all year. Lower down, that white blanket is starting to turn to slush, beginning its spring trickle into the streams and rivers that flow downhill.

Forecasters are optimistic after a relatively strong snow season, but say a variety of weather factors could limit the amount of water that will run off into rivers and reservoirs this spring.

Water managers from across the West are turning their eyes to those high-alpine climes to get a sense of summertime water supply for cities and farms across the region. The Colorado River, which supplies 40 million people from Wyoming to Mexico, gets the vast majority of its water from mountain snow. Two-thirds of that snow falls in Colorado.

Snowpack in the Upper Colorado River Basin — which includes Colorado, Wyoming, Utah and New Mexico — appears to have peaked on April 3, within a few days of the average peak date. It is measured by calculating the amount of water held in snow.

At its peak, the amount of water held in snow was right around average when compared to winters across the past three decades, and marked the second-highest peak since 2019.

A vast network of sensors, often hidden deep in the woods, gathers weather data in different parts of the Rockies, giving climate scientists and water forecasters a robust set of metrics about snow.

On the day the Upper Basin’s snowpack peaked, nearly every sensor in western Colorado and eastern Utah showed snow totals above 90% of average, with many above 100%. A handful of stations showed drier conditions, especially around the Green River in Wyoming and the San Juan River in Colorado. Both watersheds included a number of stations that recorded earlier snowpack peaks and melting periods than the rest of the region.

Hurdles on the way to the river

Even though snow totals are about average, there are a few things that stand in the way of that snow reaching rivers and reservoirs once it melts. Becky Bolinger, Colorado’s assistant state climatologist, expressed some guarded optimism about the state’s snow data.

“Living in Colorado, sometimes it's hard to have those good vibes because it can just turn on a dime,” she said.

Bolinger highlighted two big factors that could mean lower river flows than near-average snow totals might suggest.

The first is dry soil. Hot summers can sap the water out of the ground, leaving it parched when snow starts to fall. That’s the case this year, and Bolinger expects that some areas will see that thirsty dirt act like a sponge, soaking up snowmelt before it has a chance to reach rivers and reservoirs.

The second is high temperature. Abnormally warm days, which are becoming more common due to climate change, could cause that water to melt quicker and earlier before evaporating into the air. Bolinger said that is more likely in the warmer parts of southern Colorado, around the San Juan Mountains and Sangre de Cristo Mountains.

Bolinger added that windblown dust from nearby plains could land on mountain snow, causing it to melt faster, since dark colors attract more heat from the sun than pure white snow.

Looking back at El Niño

As winter turns to spring, climate scientists have a chance to compare their early-season forecasts with the outcome of this winter.

This year brought “El Niño” conditions to the Western U.S, a phenomenon that typically comes around every two to seven years. It’s a pattern driven by warm water in the Pacific Ocean, which tends to cause warm conditions in the northern part of the West and wet conditions in the southern part. It can be hard to predict the impact of El Niño on Colorado River basin snowpack because the dividing line between those two trends falls in or around Colorado.

This year, El Niño delivered less snow than expected.

“El Niño will tilt the odds in favor of wetter or snowier conditions over the region,” said Nat Johnson, a meteorologist with the National Oceanic and Atmospheric Administration. “But it doesn't rule out the possibility of the opposite outcome.

Sometimes, just the influence of our chaotic weather and the climate system can overrule the influence of El Niño.”

Johnson, who works with the agency’s Geophysical Fluid Dynamics Laboratory, said that could be the result of other patterns in ocean temperature as well as the unpredictable nature of weather.

Climate change is driving warmer days and earlier snowmelt in the Colorado River basin itself, but it also impacts faraway phenomena that influence the Southwest’s weather, making that weather harder to predict. That may have been the case with this year’s El Niño.

“Global oceans were just so incredibly warm,” Johnson said. “Not just breaking records, but really shattering the records. It just makes me think that just the really unusual warmth that we saw may have been an even bigger factor than we've typically seen in recent years.”

Planning for an unpredictable future

Data about snow, streams and soil doesn’t just matter to the people living near the mountains. It’s also watched closely by people hundreds of miles away.

"It's extremely important,” said Kristen Johnson, manager of Colorado River Programs at the Arizona Department of Water Resources. “There's no way around it. We can't have the Arizona economy without abundant snow in the Upper Basin and efficient runoff from that snow into Lake Powell.”

About 36% of Arizona’s water comes from the Colorado River. That includes sprawling farm fields near the river itself, which forms the state’s western border with California. It also includes water routed away from the river through a 330-mile canal across the desert for use in Phoenix and its suburbs.

Parts of Nevada and Southern California also rely on faraway snow to fill the Colorado River and the nation’s two largest reservoirs – Lake Powell and Lake Mead. They have both shrunk to record lows in recent years as a result of climate change and steady demand.

Changing snow patterns, driven by warmer temperatures, are at the heart of a debate about how to manage those reservoirs going forward.

Scientists say the West’s water crisis goes beyond “drought,” which is considered to be temporary. Instead, they say the two-decade stretch of dry conditions around the Southwest is a sign of “aridification” – a permanent resetting of the baseline for how much water is expected to enter rivers and streams each year.

The seven states which use the Colorado River are currently mired in a standoff about how to manage that shrinking supply in the future. They’re divided into two camps and have submitted competing proposals for how to share the river after 2026, when the current guidelines expire.

The Lower Basin’s proposal, submitted by Arizona, California and Nevada, puts forth a new system of distributing water cutbacks in times of shortage that is based on the amount of water currently in reservoirs, rather than projections for future water availability.

“Everyone's recognizing that relying on forecasts is not the best way to be making decisions,” Arizona’s Johnson said. “I think we're just looking to take the guesswork out of making those decisions in the future.”

Meanwhile, the Upper Basin states of Colorado, Utah, Wyoming and New Mexico submitted a competing proposal. It suggests entirely different management changes than the Lower Basin’s plan, but also centers around the basic fact that climate change is shrinking the snowpack that feeds the Colorado River, and people need to respond by using less water.

That plan suggests that the four Upper Basin states should be allowed to send less water to their Lower Basin counterparts. Opponents say doing so would go in the face of long standing legal agreements and may not survive challenges in court.

The plan’s authors frame it as a necessary step to alleviate the sting of climate change from those who are nearest to the snow and feel it the most.

States don’t appear close to compromise when it comes to future Colorado River management, but they’re under pressure from the federal government to find some agreement before the end of 2024 and avoid any possible complications that could be brought on by a change of presidential administrations after the November election.

This story is part of ongoing coverage of the Colorado River, produced by KUNC in Colorado and supported by the Walton Family Foundation. KUNC is solely responsible for its editorial coverage.

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