Scientists Find Snowmelt Is Accelerated By Dust, Not Just Temperature
It is over 50 degrees, and it’s mid-February here in the winter backcountry of Millcreek Canyon, just east of Salt Lake City. The snowpack is soft and slushy. And it’s melting. Whether this is climate change or not, skiers should be disappointed by this early melt-out. For millions of people living in the Wasatch front valleys below, things might be ok, but only as long as the early snowmelt can still supply enough fresh water.
Some think that warming temperatures are not the whole story here.
“There’s this popular misconception that snow melts faster because of increases in temperature,” says Tom Painter, who spoke at a TED talk last year. “Now, it’s true that that’s the case. But that’s not the primary driver. The primary driver is absorbed solar radiation.”
Painter is a geophysicist at NASA’s Jet Propulsion Laboratory and used to work at the University of Utah. He says the thing forcing snow to melt earlier is not just the temperature, but also darkly colored particles of dust.
“There are little particles in there. Little black carbon particles, dust particles, pollen, that are just slowly absorbing a little bit of radiation, and putting that into the snow.”
When dust gets blown onto the snow’s surface, Painter says it reduces the snow’s albedo, or its ability to reflect back the sun’s radiation, causing it to melt faster. About 10 years ago he and other researchers in Colorado began studying how dust from the four corners area was affecting the alpine snowpack of the San Juan Mountains in western Colorado, a major source of water feeding the Colorado river.
Chris Landry is the executive director of the Center for Snow and Avalanche Studies in Colorado.
“We recognized dust was having really significant impact on snowmelt processes here in our study area, let alone perhaps the rest of Colorado,” he said.
Back in 2003, when Painter approached Landry about wanting to study how dust affects snowmelt, there was very little science on the subject.
“Very quickly we understood that water managers in the west were most anxious to understand whether or not snow melt yields, or actual runoff quantities were being affected – especially if they were being reduced,” says Landry.
Their research showed that dust loading on the snowpack caused the peak runoff to occur about 3 weeks earlier than it had historically. But most important for western water managers, was their finding that, as a result, mountain soil and plants were exposed earlier, and consuming snowmelt water sooner. This was reducing the Colorado River’s annual runoff by more than one billion cubic meters, or 5 percent on average, each year.
Understandably, researchers back in Utah began to wonder if Wasatch Mountain snowpack’s were meeting the same fate.
Olivia Miller, a geology graduate at the university of Utah, points to satellite images of dust events.
“This is from 2009, March 4, and you can zoom in and see little plumes right here.”
The dust originates from places in southwestern Utah and Nevada, with names like the Sevier Dry Lake Bed, Milford Valley, Black Rock Desert, and the Carson Sink. Although these dried remnants of the ancient lake Bonneville are seen as one cause, lots of data show that agriculture and cattle grazing contribute greatly to soil surface disturbance, along with off-road vehicles and military training activities. Burned areas also produce dust, such as the site of the Milford Flat fire - Utah’s largest wildfire ever – that’s been a major source of dust since 2007.
“So this is down in the Sevier Desert. That is the Milford Fire scar,” says Miller. “The sources get activated down here. And they just travel with the wind, get mixed in the atmosphere, and they encounter the Wasatch Mountains, so the dust can get deposited on the snow.”
Eighty years of recorded observations at the Salt Lake airport show an average of 4.3 dust events occurring each year. Most of the events occur in the spring, when cold fronts blow in from the west. In recent years, Miller and other Utah graduate students have taken to studying the thin and brown horizontal lines of dust in the Wasatch’s backcountry snowpack.
“You can dig down and see… it’s like stratigraphy in geology. You can say ‘this event happened on January 2nd. And this event happened on February 16th.’ So you can kind of map that out. Which is pretty neat. The snowpack is great for preserving these events,” says Miller.
To verify the dust sources, Miller collected samples from the snow and examined it for traces of the chemical element strontium.
“It’s kind of like a fingerprint. You can use it as a tracer. So the strontium in the dust, you can tell where that dust source was.”
She then took core samples from older trees nearby in the Wasatch Front canyons.
“Most of the strontium that trees take up is from dust,” says Miller. “Like 90-percent in some cases. So the dust is really having a big impact on the ecosystems here.”
Miller’s findings indicate that dust has always been a part of the Wasatch Front ecosystem. Indeed, environmental scientists increasingly recognize dust as an important player for ecosystems around the world. But how a more quickly melting snowpack will affect the ecology of the Wasatch remains a question.
“This is preliminary, but what we’re seeing is there’s a longer growing period and longer flowering period,” says Lafe Connor, a doctoral student at Brigham Young University.
Connor wanted to see how soil and plants would respond to a faster melting snowpack. He scattered dust over plots to force early melting at two different elevations in Fairview Canyon in Sanpete County. And he saw that after the snow melted early, plants flowered early, which meant sometimes they aborted their flowers when the soil water also went dry early. He says this leads to more questions about the impacts on pollinators, for example.
“There could be disconnect between when plants flowers, and when the pollinators arrive, like hummingbirds… is that going to affect the hummingbirds when they arrive? Are they going to have the same resources that they need,” asks Conner. “It’s an important thing to understand, are these systems going to be disrupted.”
Rick Gill, a professor at BYU adds, “So what we see is we have these interacting processes. The timing of snowmelt isn’t just what happens right after snowmelt, but how that sets up the entire growing season in terms of water availability.”
Gill and others at BYU plan to work with other Utah researchers through a collaborative project to continue to study soils and plants, as well as the quality and quantity of snowpacks along the Wasatch front beginning this year. Zach Aanderud is professor of plant and wildlife sciences at BYU.
“We are also measuring the dust, the albedo of the dust… modeling per se how that is potentially changing the water availability patterns in these three watersheds across the Wasatch front. We have real-time instruments measuring flow is one the big ones. So we can hopefully start linking dust to see how much water is in these different watersheds,” says Aanderud.
Utah scientists seek to share with water managers the connections that link deserts and dust, with snowpacks and water.
There is a renewed sense of urgency since signs point to an even drier and dustier future, as scientists predict temperatures will increase by up to 7 degrees by the end of the century. Meanwhile, proposals like Nevada’s Snake Valley water pipeline, threaten to parch another patch of desert by pumping groundwater near the Utah border, to Las Vegas.
With growing populations, and rising temperatures, the dust is not likely to settle when it comes to fighting for water in the west.
This is the first story by Explore Utah Science in a series called “follow the flow”, that examines ongoing research to maintain the sustainability of Utah’s precious watersheds.