Dust-on-snow update: 2013 moisture could mean a dusty spring


Dust has become a major concern for climatologists – and anyone who drinks water that comes from mountain runoff – in recent years. Yet while dust storms are cropping up in the eastern parts of the state this winter, the Colorado Dust-on-Snow Program (CODOS) on the Western Slope has yet to report any dust-on-snow events in 2014. In fact, there hasn’t been any dust recorded at a major study site at Red Mountain Pass in southwestern Colorado since September.

According to director Chris Landry, that's not too unusual about having no dust at CODOS thus far in 2014. And even if the recent drought conditions bring CODOS its first-ever January dust-on-snow event (that’s when dust blows onto snow and expedites melting), early season dust isn’t that problematic. When dust settles late in the season, say March, April, or May as is common, it has a bigger impact, since there's more snowpack to melt off.

The Senator Beck Basin study site measures dust-on-snow events in the San Juan Mountains. Photo courtesy of the Center for Snow and Avalanche Studies.

Although dust on snow is becoming an increasingly stress-inducing topic for water managers, at least our winter snowpack is still not being dusted. Yet disaster could still strike this spring. It remains to be seen whether all the rain that fell late in 2013 will lead to more dust a few months from now. USGS geologist Harland Goldstein says that heavy rains – like Arizona's unseasonable late-November soakings – deposit sediment that, since it's unvegetated, can easily  blow away.

Nestled in the western San Juan Mountains, the first major mountain system downwind of the Southwest's vast deserts, the CODOS program at the Center for Snow and Avalanche Studies in Silverton is aptly placed to monitor warming, drought, precipitation and other processes that affect the whole region’s environment. As a general rule, no dust at CODOS means no dust in the rest of Colorado’s mountains.

Here's how it works: When dust collects on snow at the Senator Beck Basin near Silverton, Colo., CODOS takes samples and sends them to scientists at Goldstein’s USGS lab in Denver, who analyze its particle size, distribution and chemical makeup of the dust, combining the analysis with satellite imagery of blowing dust events to pinpoint the dust's origins.

Anytime you see dust on snow and you see that red or brown, that’s the iron oxide giving it that color,” Goldstein says – iron oxides like goethite and hematite, which are ubiquitous in the Four Corners. Even just a slight darkening of the snow’s surface will decrease the snow’s albedo, or its ability to reflect sunlight back into the atmosphere, and thus increase melting.

Reddish-brown layers in the snowpack chronicle a season of dust-on-snow events in the snowpack. Photo courtesy of the Center for Snow and Avalanche Studies.

Given the potential impacts of albedo on climate change, dusty snow certainly has the attention of climatologists – and because snowpack feeds many of the West's major rivers, dust is problematic for water managers as well. Decreased albedo can lead to earlier snowmelt and runoff coming all at once rather than over time, which can overwhelm reservoir storage capacities and cause flooding. Landry references one particular dust-on-snow event in spring 2011 that fell on “tremendous snowpack," resulting in extreme melting and flooding in the Yampa River Basin. Another event last April deposited more dust than any other single recorded event, increasing the rate of snowmelt with moderate to severe effects across several vulnerable water districts.

Eight southwestern Colorado water districts with snowpack vulnerable to dust, including the Yampa, help fund CODOS, and use the station’s reports to inform their water management strategies. As compared with this date last year, the Yampa and White River Basin currently sits at 112 percent of median snowpack, but only at 59 percent of its median annual peak snow water equivalent, or how much water it will get from the snow. Snowpack at Red Mountain Pass is at 99 percent of the median, and will slip unless it snows soon. The Upper Rio Grande Basin is at 71 percent of median snowpack for the date, but only 39 percent of their water equivalent. The San Miguel, Dolores, Animas (which includes Red Mountain Pass) and San Juan River Basins hang at 40 percent snow-water equivalent, as well.  Even a single major dust-on-snow event can impact water supply, making complex networks of water appropriation rights even more challenging to manage.

“We’re definitely in a West-wide dry pattern right now, and it’s not getting better at this point because there’s no precipitation falling anywhere,” says Colorado state climatologist Nolan Doesken. Last spring was the fifth driest on record for the Four Corners states and the third consecutive season with below-normal precipitation, and the region has been in and out of various stages of drought for several years.

“Considering that this weather pattern has left California high and dry for the entire first half of the winter, I almost consider ourselves lucky that we got as much snow as we did,” Doesken says, adding that Colorado is likely to stay dry into early February.

If we do see dust blowing in from eastern Utah and northern Arizona to the Colorado Rockies this winter, Landry says it would be better to get it sooner rather than later. If big dust storms hit the snow before storminess returns – before more snowpack can accumulate – then theoretically, the effects on albedo, snowmelt and runoff would be less severe. But according to Landry and CODOS data, that sort of convenient timing “isn’t even remotely likely.” We’re most likely to see a healthy dusting come spring.

Christi Turner is an editorial intern at High Country News.  She tweets @christi_mada.

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