New study shows how helping desert soil could save our snow

 

It’s the start of snow season, which means that everyone who cares about water is keeping an eye on the mountains, anticipating how long we’ll ride the wave of snowmelt into next summer. The runoff season is never as predictable as anyone would like, but in the last decade or so there’s been a new wild card that makes the snowpack’s bounty seem even more capricious – spring dust storms.

Southwest Colorado’s snowpack is the West’s hardest-hit when spring winds carrying tiny dust particles slam into the mountains. That cinnamon layer coating the snow means that it absorbs more of the sun’s radiation, heats up, and melts faster than clean snow (it’s the black t-shirt versus white t-shirt effect). As water managers in the Colorado Basin plan for the region’s impending water crunch, and more dust is blowing around the West, they are starting to realize that dust is a hydrological game-changer.

The Center for Snow and Avalanche Studies, in Silverton, Colo., began tracking dust on snow in the San Juan Mountains in 2003, but dust has been worse in recent years, including 2013. In a recent study looking at the combined impact of climate warming and dust on the Upper Colorado River Basin's snowpack, researchers found that “extreme” dust years like 2009 and 2010 advance spring runoff timing by three weeks, compared to moderate dust years. That’s a total of six weeks earlier than runoff from clean snow.

That doesn’t bode well for water users or for ecosystems. Normally, snow doles out water gradually over the spring and early summer, but when dust spurs snow into early melt-out, that gives soils a head start on drying out in the summer and irrigators are more likely to end up water-short later in the season.

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Dusty snow in the San Juan Mountains, 2013. Courtesy of the Center for Snow and Avalanche Studies

That result adds more detail to what earlier research has shown – that at least in the short term, dust has a bigger impact on the speed of mountain snow melt than increasing temperatures do. While the new study was based on a model covering the Upper Colorado River Basin, at a snow monitoring site on Red Mountain Pass near Telluride, dust from the 2009 and 2010 storms advanced melt by 50 and 43 days compared to a clean snowpack. “It’s as if somehow you had magically added two to four degrees Celsius to the temperatures we experienced during those years,” says Chris Landry, the executive director of the Center for Snow and Avalanche Studies.

Dirty snow also impacts the amount of water the mountains provide, because it leaves soil and plants exposed longer, allowing water more time to evaporate.

Even without dust hastening the snow’s departure, climate and population growth projections for the Colorado River, which serves 40 million people in 7 states and Mexico, are startling. The amount of water promised to users already exceeds what’s available, and the region is staring down climate projections that point to runoff declines of 5 to 20 percent by the mid-21st century.

Cleaning up the snowpack could be an immediate way to buffer the region’s water supplies against climate impacts, and reintroduce some predictability back into the runoff season. Returning snowpack to pre-mid 1800s dust conditions would more than mitigate the changes in runoff timing expected from climate warming by 2050, according to the recent study. Keeping dust at a “moderate” level would offset the earlier runoff by 10 days by 2050 and 20 days by 2100, under a moderate to extreme greenhouse gas emissions scenario.

But that raises the next question: How do you knock dust levels back to what they were before we started tearing up Western soils? First you have to know where it’s coming from. There have been massive dust storms around Phoenix and Tucson in recent years, like the haboob that swallowed Phoenix in 2011. Abandoned cotton fields have taken a lot of blame – but those aren’t the main culprits soiling Colorado’s mountains.

By using satellite images and matching the chemical signatures of dust on snow back to its original landscape, dust gurus have figured out that winds are picking soil up from disturbed desert areas in Arizona, Utah and New Mexico (and increasing aridity isn’t helping). Most of that is coming from the Colorado Plateau, and Milford Flat – the site of Utah’s largest wildfire – is a chronic contributor, according to Jayne Belnap, an ecologist with the U.S. Geologic Survey in Moab, who was involved in the recent study.

The problem with tracking dust sources is that the big contributors like Milford Flat are easy enough to see in satellite imagery, but the small and medium ones, like dusty dirt roads, abandoned housing developments, or overgrazing, are harder to pinpoint. It takes many years of data, which Belnap doesn’t have yet, to say “grazing does this, and roads do that.”

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A dust storm hitting Silverton, Colorado. in spring 2013. Courtesy of the Center for Snow and Avalanche Studies

But she thinks they do know enough about certain areas to start restoring loose soil now. People think of deserts as dust and sand, but when they are healthy, they are stable, and their soils don’t tend to blow away.

Beating back dust ultimately comes down to the slogan found on National Park signs around the Southwest: “Don’t Bust the Crust.” That refers to the cryptobiotic soil crust that Belknap studies and that anchors the desert ecosystem, and its soil, in place. “The obvious thing is to stop disturbing it, of course, but we have the problem of the West being the bull's-eye for energy, wind, solar, and everything else,” she says.

But if an area has become too desertified, it needs fencing or wind breaks to help hold the sand in place. Even though federal land agencies, like the Bureau of Land Management, are aware of these issues, the funding isn’t there to help get the work done.

It’s hard to quantify how much it would reduce the overall dust problem, but since it will lock out soil-disrupting motorized use and energy development, a massive, contentious wilderness deal being negotiated in Utah right now could have “huge implications” for minimizing dust,” Belnap says. But the deal won't solve all of our dust problems. And regardless of the policy for managing arid landscapes, she says, “we just need to take dust seriously.”

Sarah Jane Keller is an editorial fellow at High Country News. She tweets @sjanekeller.

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