Dust on snow reducing Colorado River flows by accelerating spring snowmelt

“Annual runoff is lower by more than 5 percent on average”

This is Part 1 of a three-part series looking at the widespread impacts of dust-on-snow on the Colorado Mountains, both in the Gunnison Basin and the Colorado River Basin as a whole. Parts 2 and 3 will focus on the affects on recreation and what measures water managers are taking to deal with decreased water supplies.

Blame it on 150-plus years of grazing on the Colorado Plateau, recreation wreaking havoc on delicate desert soils, or just bad geographic positioning. Any way you cut it, desert dust is finding its way to the local mountains each spring, and depositing a dark, dirty layer on the snowpack that absorbs sun instead of reflecting it. That leads to faster snowmelt than usual, and a litany of environmental issues that last all year long.
For example, in-stream flows in the Slate River are currently below the minimum 23 cubic feet per second. The Colorado Water Conservation Board has recently put a “call” on (requested more water be released for) the Slate River because the in-stream flows are not being met, which means water will need to be released from Long Lake. On a larger scale, annual runoff feeding the Colorado River has decreased 5 percent over the last 150 years.
 
Eye-Opening Impacts

The aesthetic effects of dust-on-snow are visible at face value, especially during the spring.
Red-brown zebra stripes and broad swaths of dirty snow blanket the mountains during spring, affecting backcountry skiing and potentially adding to avalanche hazard.
But the effects on water supplies run even deeper, and longer—as in the length of the Colorado River. A study funded by NASA and the National Science Foundation (NSF) and published in last week’s Proceedings of the National Academy of Sciences concluded the following: Snow melt in the Colorado River basin is occurring earlier, reducing runoff and the amount of crucial water available downstream. The new study shows this is due to increased dust caused by human activities in the region during the past 150 years. In addition, peak spring runoff now comes three weeks earlier than before the region was settled and soils were disturbed. Annual runoff is lower by more than 5 percent on average compared to pre-settlement levels.
According to the report, the findings have major implications for the 27 million people in the seven U.S. states and Mexico who rely on the Colorado River for drinking, agricultural and industrial water.
Tom Painter, a snow hydrologist at both NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and the University of California at Los Angeles, led the research team. His team examined the impact of human-produced dust deposits on mountain snowpacks over the Upper Colorado River basin between 1915 and 2003. Studies of lake sediment cores showed the amount of dust falling in the Rocky Mountains increased by 500 percent to 600 percent since the mid-to-late 1800s, when grazing and agriculture began to disturb fragile but stable desert soils.
The NASA press release explains why dust on snow is such a downer for water supplies.
“More than 80 percent of sunlight falling on fresh snow is typically reflected back into space. In the semi-arid regions of the Colorado Plateau and Great Basin, winds blow desert dust east, triggering dust-on-snow events. When dark dust particles fall on snow, they reduce its ability to reflect sunlight. The snow also absorbs more of the sun’s energy. This darker snow cover melts earlier, with some water evaporating into the atmosphere. Earlier melt seasons expose vegetation sooner, and plants lose water to the atmosphere through the exhalation of vapor. The study shows an annual average of approximately 35 billion cubic-feet of water is lost from this exhalation and the overall evaporation that would otherwise feed the Colorado River. This is enough water to supply Los Angeles for 18 months.”
According to lead researcher Tom Painter, “The compressed mountain runoff period makes water management more difficult than a slower runoff,” Painter said. “With the more rapid runoff under dust-accelerated melt, costly errors are more likely to be made when water is released from and captured in Colorado River reservoirs.”

Local Flows

For local perspective, the Bureau of Reclamation’s draft Annual Operating Plan for Colorado River Reservoirs 2011 includes detailed information on the Aspinall Unit (Blue Mesa, Morrow Point and Crystal Reservoirs).
According to the plan, below-average snowpack conditions prevailed in the Gunnison Basin during water year 2010. Snow measurement sites in the basin reported mostly below-average snow water equivalent levels throughout the winter and into the spring of this year. The April through July unregulated inflow into Blue Mesa Reservoir in 2010 was 0.494 million acre-feet, which was 69 percent of average. Water year 2010 unregulated inflow into Blue Mesa Reservoir was 0.737 million acre-feet, which was 74 percent of average. Blue Mesa Reservoir did not fill in 2010. Under the minimum probable inflow scenario, Blue Mesa Reservoir is not projected to fill in 2011.
High Country Citizens’ Alliance (HCCA) water program director Steve Glazer said locally, dust on snow is nothing new, but it’s getting worse. “I’ve lived here 41 years, and known about this issue that whole time. Every spring the wind picks up and we get a red layer on snow. It’s not a new phenomenon—some years it’s more pronounced than others. I knew the situation was not improving, but getting worse.”
Mitigating the causes of dust on snow is a monumental task. According to the NASA press release, Painter believes steps can be taken to reduce the severity of dust-on-snow events in the Colorado River basin. He points to the impact of the Taylor Grazing Act of 1934 for potential guidance on how dust loads can be reduced. The act regulated grazing on public lands to improve rangeland conditions. Lake sediment studies show it decreased the amount of dust falling in the Rocky Mountains by about one quarter.
Chris Landry, director of the Center for Snow and Avalanche Studies in Silverton, Colo., has been at the forefront of dust-on-snow research from the beginning, along with Painter. He also contributed to the Colorado River flow study, and conducts much of the fieldwork involved in collecting dust-on-snow samples from around the state of Colorado.
“The CSAS will be sending dust samples direct to the U.S. Geologic Service [USGS] to try to figure out where this dust is coming from more precisely, and thinking about which locales might be the most important to think about mitigating, but that’s way down the road,” Landry said. “It’s going to require a few years of observation to pinpoint, or generally pinpoint some parts of the greater Colorado Plateau as the primary source areas, if that’s even possible. There’s a lot of further monitoring and remote sensing to be done before there could be any focused effort to address the emission end of the deal. That is the focus of the USGS team, on the emission side of this equation.”
“We need to get the agencies that control those lands where this stuff is originating from to do something to reduce the impact,” Glazer said. “What’s alarming is how startling its impacts are becoming—the results are obvious and documented.” Glazer cited areas in southeastern Utah and the Navajo Reservation in northeastern Arizona as two likely source areas for the dust that falls on local peaks.
“The Bureau of Land Management [BLM], the agency managing these lands in southeastern Utah, needs to be slapped on the hand, because they are impacting us and being irresponsible by not addressing the issue,” said Glazer. “They are causing unintended consequences outside their jurisdiction and that cannot continue.”
Mitigating the problem at the source will require a multi-faceted approach, starting with identifying the exact source area, if that’s even possible.
“Restoration of desert soils could increase the duration of snow cover, simplifying water management, increasing water supplies and reducing the need for additional reservoir storage of water,” according to Painter. “Peak runoff under cleaner conditions would then come later in summer, when agricultural and other water demands are greater. It could also at least partially mitigate the expected regional impacts of climate change, which include reduced Colorado River flows, increased year-to-year variability in its flow rate and more severe and longer droughts. Climate models project a 7 percent to 20 percent reduction in Colorado River basin runoff in this century due to climate change.”

Stay tuned for the next couple of weeks as we continue to examine the dust-on-snow phenomenon.