Fine soil from the Southwest is robbing the Colorado River of critical snowmelt. A scientist who monitors dust’s impact on snow wants state and federal leaders to take a closer look.
May 18, 2023
The story Susan Behery tells about dust blowing into Colorado from New Mexico and Arizona sounds almost Biblical, like cows dropping dead in their owners’ fields or swarms of locusts devouring their crops.
A hydraulic engineer for the Bureau of Reclamation in Durango, Behery says she once saw dirt falling from the sky in the manner of rain. It was so heavy, she said, it splatted when it hit the ground. When the storm that brought it moved on, a brown residue covered Behery’s car, her lawn furniture, her house. In fact, it covered the town of Durango, the town of Silverton and the San Juan Mountains, where Behery’s colleague, Jeff Derry, does the bulk of his work as the executive director and lead scientist for the Center for Snow and Avalanche Studies and its Dust on Snow program.
Behery says she and Derry work closely together. This time of year they talk by phone almost daily. That’s because Derry studies dust that travels to Colorado from northern New Mexico and Arizona. When it arrives here, in storms stopped short by the mountains, it settles in a distinct brown layer on the snow.
Derry’s main job is monitoring the dust layer (or layers) for water managers like Behery, because dust on snow is a major contributor to how much of the water in Colorado’s snowpack reaches the creeks, rivers and reservoirs that serve our state, and when the flows of those creeks and rivers reach their peak. That, in turn, impacts how Behery and her colleagues in water management control things like the levels of river water flowing into and out of reservoirs, of which Colorado has many.
The primary stem of the Colorado River has 15 dams and its tributaries have hundreds more. Each major tributary flows out of a river basin reliant on snow. “But we’ve been having these sporadic good precipitation years with lots of drought in between,” Behery says. And drought years lead to low snowpack, which, when coupled with dust, disrupts rivers.
When that happens, millions of people, animals and fish are directly impacted, says Behery. The vast majority don’t know it, Derry adds, but maybe they should.
According to a 2010 paper about the history of dust on snow by Thomas Painter, Jeffrey Deems and Jayne Belnap, climate models at that time predicted runoff losses of 7%-20% in this century due to human-induced climate warming.
Additionally, Derry says long-term trends based on data he has collected since 2003 show dust-on-snow is also wreaking havoc on flows in the Colorado River’s headwaters. But we can’t really stop dust from piling up on Colorado’s snowpack. And that’s a problem Derry says more people should know about.
Dust origination and politicization
The paper showing those haunting statistics about runoff losses also shows that by the late 1880s, decades prior to allocation of the Colorado River’s runoff between seven Western states in the 1920s, “a fivefold increase in dust loading from anthropologically disturbed soils in the southwest United States was decreasing snow albedo and shortening the duration of snow cover by several weeks.”
Understanding snow albedo takes some mental gymnastics. But as Derry puts it, when a dust layer settles on the snow, like a dark T-shirt, it absorbs the sun’s light and heat into the snowpack. And when the snow is free of dust, it reflects the light and heat back into the atmosphere. So high albedo leads to slower snowmelt and lower runoff, while low albedo leads to faster snowmelt and a higher runoff.
The paper also mentions dust shortening the duration of snow cover, and that’s a different process. Derry says as dust causes earlier snowmelt, plants and soil are exposed earlier in the spring. Increased exposure to the air and sun causes the soil to dry out through evapotranspiration, or the process by which water is transferred from the land to the atmosphere by evaporation from the soil and plants exhaling water vapor. “And that could have been water in the snow that would flow into streams,” he says.
The anthropologically disturbed soils of the 1800s and 1900s, however, were coming from poor farming techniques and vast numbers of cattle chewing up the landscape, Derry adds.
Jayne Belnap, a retired USGS soil ecologist with expertise in desert ecologies and grassland ecosystems, says those problems continue. “All low-elevation desert surfaces are stable until you disturb them,” she says. But when disturbance occurs —“by animals, bikes, cars, plows, feet,” she adds — the extremely fine soil that surfaces is perfect for flying on the wind to Colorado.
Desert surfaces aren’t naturally dusty places; they’ve just been grazed, plowed, recreated and prodded for oil and gas reserves to sandy soil devoid of nutrients, Belnap says. One solution to keep more soil intact is a change in government policy that holds whoever is degrading the soil accountable. Belnap says this includes anyone in the desert regions of northern New Mexico and Arizona who actively disturbs the protective surface of the desert. Derry adds that in the problem region, “there are a lot of federal land owners, and as far as I know, there’s no concerned effort to mitigate the problem.”
Then there’s the issue of liability, says Belnap.
“The soils between Tucson and Phoenix, which were plowed for cotton, went from coarse sand to silt. You can drive off the road, throw up a handful and it just hangs in the air,” she says. “When that’s disturbed, it blows across the highway and kills people. But in order to stabilize an area, the people in charge have to admit there’s a problem, and no one will. We finally got a congressman to get all upset about it, but if he says Joe rancher is creating a huge part of the problem, what’s Joe rancher gonna do? He’s gonna sue.”
What all of this amounts to, for now, at least, is people like Behery having to continue factoring dust into the way they manage Colorado water.
And in years like 2022, that meant being ready for some interesting flows.
Dust’s impact on Colorado’s water
In the spring of 2022, “the soil was ridiculously dry, the snowpack was terrible and windstorms blowing into Colorado from the south kicked all the dust up and deposited it all over our mountains,” Behery says.
That led to “snowpack running off early and in an extreme way, high-intensity, low-duration flows” and dropping river levels “that left us almost no base flows in the end of May-early June, when we had irrigation season coming online, which is when I have to release a lot of water,” she adds.
“So the severity of dust just really affects things. You never knew dirt could be so interesting, did you? People are like, ‘Dirt and dust. So icky.’”
But much rests on Behery’s releases of water from Navajo Reservoir, which spans the Colorado-New Mexico border southeast of Durango. Beneficiaries include endangered fish, which rely on certain flows to make it to their spawning grounds and to find food. Navajo Reservoir water also helps farmers downstream slake their crops and water their animals. And eventually, some flows into the San Juan River and on to the confluence with the Colorado River above Lake Powell, which with Lake Mead, serve millions of people who live in Arizona, Nevada and California.
That’s why Behery leans so heavily on Derry’s data from his main study site, in Senator Beck Basin, in the western San Juan Mountains between the towns of Silverton and Telluride.
Every winter through peak runoff since Derry took over the dust-on-snow study from his predecessor, Chris Landry, he has strapped on climbing skins and skied to the study site several times a week. Using a trusty shovel, a magnifying glass, a snow-water equivalent tube and a thermometer, he measures snow crystals, snow temperature and how much water the snowpack contains, before he checks the sensors of his backcountry climate station for albedo levels to provide an “albedo forecast.”
Since 2019, he has sent this information to Behery to indicate what she can expect to see downstream “in the next 1, 2, 3, 5, 7, 30 days in the future,” he says.
The Center for Snow and Avalanche Studies is the only entity that monitors dust-on-snow conditions on an operational basis for the water community, researchers and stakeholders in the United States. The dust-on-snow program is a statewide effort, with 11 river basin monitoring sites from which Derry and a team of interns assess the density of dust on snow and report on local snowmelt and streamflow impacts to the corresponding watersheds.
Last year, with several major dust events, Derry’s data was especially prescient, Behery says. But this year isn’t so bad, “because we have a pretty wet situation in the Southwest. So even if we do have a lot of windstorms it probably won’t pick up as much dust in the past,” she adds.
But she’s still calling Derry, or he is calling her, daily or close to daily, and she’s using his data to help best predict peak flows. Water releases by Behery and other river managers from McPhee Reservoir on the Dolores River impact all of the normal stakeholders, plus Colorado’s boating and fishing communities. And Behery says for each type of release the hydrograph must have the “perfect shape.”
“For example, it needs higher flows (correlating to a different shape) on weekends when people are going to recreate,” she says. “The same goes for Memorial Day. And dust is always a part of the equation, because if it’s really dark and the sun is shining, we’ll have all of this runoff happening. And then we have a cool-down, and that will stop the runoff and we’ll think it has ended. But if you look at Jeff’s data, it hasn’t ended. There was just an inch of snow on top of the dust, which increased the snow’s albedo and slowed down the runoff. We’ll still have more coming, so we’ll know what to do with the boater spill. We can keep it coming. We don’t have to shut it off.”
But managing water like Behery does “is real-time fuzzy science,” she adds. “It’s what I call riding the dragon, because you’re just trying to stay on it. There are lots of decisions and lots of Monday morning quarterbacks.”
Behery’s water updates go out to 450 people,“internal, external, public, stakeholder and private,” she says. She coordinates with Derry to make the best-informed decisions. “Our goal is to make sure everyone is getting their fair share of water,” she adds. And this year is no different, although the snow is deeper, the temperatures cooler, the winds calmer and there’s less dust.
A dust scientist’s plea to Colorado senators
In fact, of the six Colorado dust events so far this season, the only major one occurred April 3.
Most of that event bypassed the Senator Beck study site and continued north, toward Aspen. There, at Grand Mesa and at Beaver Creek, people reported seeing a “gritty, dark layer” that even after new snow had covered it, skiers’ tracks resurfaced. But in Derry’s dust-on-snow update for April 6, he wrote, “I guess we all knew [a significant event] would happen eventually.”
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The event turned out to be widespread and nasty in terms of the amount of dust deposited on a relatively pristine snowpack that had essentially reached maximum accumulation, he reported. “It just takes one bad dust event to change things — this one will change the characteristics of snowmelt and runoff for the duration of spring dramatically.” The dust put places that received it in the “average” category.
But in the San Juan basin, which Behery manages, even given this event, things are looking a little better than normal.
“In a year like this where we have a good snowpack, the dust cycle continues but we can have a reset,” she says. “Still, we need subsequent years of snowpack and runoff that are either average or above average to make a lasting impact. People think one year can do it, but we’ve had 20 years of drought with a few little good years in between.”
Derry told The Sun that he’s part of a “small, loose group” of scientists, landowners, land managers and others working to build a coalition that can define the problem with and potential solutions for dust and then encourage those who own the lands dust originates on — including the BLM and Bureau of Indian Affairs — to take action through policy and support. His motivation for helping start the coalition “is when I give talks to groups — doesn’t matter who — and explain what I do, always, the first question I get is, ‘We know what the problem is, why don’t we fix it?’ And I am like, ‘Yeah, why don’t we?’ so this is my attempt.”
At the end of his April 6 update, he also addressed Sens. John Hickenlooper and Michael Bennet, who were traveling through Colorado with senators from other Colorado River Basin states to see and discuss river issues and solutions. “It would be valuable if the group were to swing through the Southern Colorado Plateau and discuss the imperative need to restore soil health for the benefit of the land itself, the quality of life and livelihood of the people who live in the region, and of course to minimize dust transport to the Colorado snowpack,” Derry wrote.