CREDIT: Jeffrey Deems
GOLDEN, COLORADO — The deep snow cover in Colorado’s mountains, well above average this year everywhere except the southern part of the state, is melting and running off very quickly in June. It’s an annual event that is watched closely by farmers who depend on irrigation water, water managers eager to see their reservoirs filled, kayakers and rafters looking for white water thrills, and increasingly by scientists looking at how the West is doing in a warming world.
For about the last decade, a small group of researchers has been studying a particular aspect of the annual snowmelt in the Colorado Rockies: how it is affected by dust that blows in from Arizona, southern Utah, and other points in the desert Southwest and settles in layers on the mountain snow. In part, their research is driven by the huge importance of the mighty Colorado River, which begins high in the Rockies and ends its long journey in Mexico.
Along the way, the Colorado provides water for some 40 million people, and more than five million acres of cropland in some of the richest agricultural regions in the U.S.
“The dust sits on top of the snowpack, it absorbs more solar radiation and you get melting sooner,” said Brad Udall, a senior fellow at the Getches-Wilkinson Center for Natural Resources, Energy and the Environment at the University of Colorado. That dust has a surprisingly large influence on both the timing of the annual runoff and the amount of water that ends up in the already stressed Colorado River system.
A study published in 2010 in the Proceedings of the National Academy of Sciences found that heavy loads of dust in the Colorado mountains had moved the period of peak snowpack runoff ahead by three weeks compared to pre-settlement in the mid 1800s. Accelerated melting is bad news for farmers and water managers who rely on the melting snowpack to deliver water steadily throughout the year; the Upper Colorado basin has few reservoirs to store excess water in the case of a rapid melt.
CREDIT: Jeffrey Deems
Earlier runoff also means earlier exposure of soils and earlier plant germination, which increases both evaporation of water in the soils and transpiration of water from plants. This phenomenon, known as evapotranspiration, is costing the Colorado River basin about five percent of its annual flow, or some 800,000 acre feet, according to the PNAS study. That is more water than is used annually by the cities of Las Vegas, Denver, Phoenix and Tucson combined.
That news, based on field research between 2005 and 2008, was startling enough, but it quickly got worse. In 2009 and 2010 “unprecedented levels of dust loading on snowpacks in the Upper Colorado River Basin” were observed and amounted to about five times the dust depositions in the 2010 study, according to a 2013 paper published by some of the same authors in Hydrology and Earth System Sciences. The researchers said that the additional dust loading moved peak snowmelt ahead by another three weeks, for a total of six weeks earlier, and reduced the flow of the Colorado River by a total of six percent.
Even though much of the Southwest and Great Basin have been arid for a long time, those areas didn’t produce a lot of dust until the West was settled in the mid to late 1800s and settlers brought in a lot of livestock.
“Most of the land surface in the desert southwest is naturally covered by crusts,” said Jeffrey Deems of the Cooperative Institute for Research in Environmental Sciences, a joint institute of the National Oceanic and Atmospheric Administration and the University of Colorado. “Those crusts protect the soil surface from wind erosion and thus make the natural surface not very prone to erosion.”
From studies of lake sediments, Deems and other scientists know what happened when the settlers and cowboys arrived and millions of grazing animals began breaking that soil crust: about a 700 percent increase in dust. By the 1930s, when better controls were placed on grazing by the federal government and herds were reduced, that increase had fallen to about 500 percent and remained at that level through many decades.
Snowpack monitoring by the Center for Snow and Avalanche Studies in the San Juan Mountains of southern Colorado since 2003 suggests that dust is now becoming more of a problem, though Deems says “we are hesitant to say whether this is cyclical or whether this represents a steady increase … But if we observe dust on snow and other proxies, it does look like it is getting worse over the past couple of decades.”
And it’s getting worse at the same time that climate change is ushering in profound changes for the American Southwest that are likely to include more erosion and more dust.
Climate change, according to the USGS, “will have profound effects on water and living systems in the Colorado River Watershed,” where models predict a decrease in precipitation this century of as much as 20 percent and a temperature rise of as much as six degrees Celsius. “Increased warming is expected to decrease runoff by up to 30 percent through the 21st Century,” according to the USGS, at the same time that populations in the region are climbing.
The landmark National Climate Assessment, released in April, had many of the same dire predictions for the future of the Southwest in a changing climate — making the already parched region hotter and drier. “Increased heat and changes to rain and snowpack will send ripple effects throughout the region’s critical agriculture sector, affecting the lives and economies of 56 million people — a population that is expected to increase 68 percent by 2050, to 94 million,” the report warned. “Severe and sustained drought will stress water sources, already over-utilized in many areas, forcing increasing competition among farmers, energy producers, urban dwellers, and plant and animal life for the region’s most precious resource.”
And many of these impacts are not far off in the future, they are already underway. The Colorado, said Deems, “is already a stressed and over-allocated river, demand already exceeds supply, and that is only going to get worse.” In the upper part of the Colorado River basin, Deems noted, there are few reservoirs to store water and the mountain snowpack serves as storage. With dust making runoff come so much earlier, “if you are a water user, all of a sudden you are looking at a two-months longer dry season.”
“The dust is the result of all these human activities, from construction, to off-road vehicles, to grazing, any kind of land use disturbance that breaks up the soil,” said Udall. “This is local, it’s not from China, it’s from the Southwest.”
The fact that we, in our land management activities, are responsible for much of the dust in the West means that there are also opportunities to mitigate it by changing the way we do things. “We still have the capability, even if climate change is doing bad things to the snowpack, we still have the opportunity to reduce the impact of dust on snowmelt timing and to preserve snowpack until later in the season,” said Deems.
While satellites make it easy to see where the major dust storms are coming from, the smaller, chronic sources are harder to detect, says Jayne Belnap, an ecologist with the U.S. Geological Survey in Moab, Utah. Last year she set out to measure how dirt roads contribute to the problem and found that they produce “a significant amount of dust,” and that the better the roads, the bigger contributors they are.
With the surge in oil and gas development in the West, which is accompanied by lots of road construction to service the drilling and production phases, Belnap’s research suggests that changing the way we build dirt roads can make a significant difference in how dust affects the Colorado River. “The faster you can drive on them, the more dirt” becomes airborne, said Belnap. “We need to keep those dips and doodles and curves in there.”
Belnap has found another significant dust source in fallow agricultural fields in Arizona and Texas, particularly former cotton growing lands between Phoenix and Tucson that have been abandoned because of high water costs. “They were plowed so much they’re like talcum powder…they just blow.” That source can also be mitigated with plant cover, says Belnap, pointing to successes in China with stabilizing moving sand dunes by putting small physical structures in fields to allow native plants and shrubs to take hold.
“You can manage this, you just have to have the political willpower to do it,” Belnap said. “Dust has to become part of your land management goals.”
One of those goals should be conserving big chunks of western land and keeping oil and gas development and off-road vehicle use at bay, said Mathew Gross of the Southern Utah Wilderness Alliance. Gross’ group is pushing for creation of a Greater Canyonlands National Monument as a 1.4 million acre buffer around Canyonlands National Park.
“If industrial development comes to the greater Canyonlands, it will exacerbate the effects of dust on snow,” Gross said. “That has consequences all the way to the Imperial Valley of California.”
The relatively small local impacts of dust — multi-car pileups on Arizona highways, health issues like Valley Fever — are unlikely to grab the national spotlight, Belnap said. What will, she believes, is more widespread worry about reductions in water availability and reliability in the Colorado River system.
“If your lettuce doesn’t get grown in California, you notice that in Washington, D.C.,” Belnap said. “So dust in the West becomes a national issue.”