Dust on snow, earlier runoff? #COdrought

Dust streaming across Four Corners April 29, 2009 via MODIS
Dust streaming across Four Corners April 29, 2009 via MODIS

Here’s a look at the problem of dust on snow affecting the timing of runoff, from John Peel writing for The Durango Herald. Here’s an excerpt:

The issue is this: During the last two decades, an increasing amount of dust, mostly blown via storms from northeast Arizona and southeast Utah, has landed on Colorado during the winter and, more often, spring. This dust settles on the snowpack, causing the snow to lose much of its ability to reflect the sun…and escalating the rate of melt drastically.

It’s a situation everyone from water managers to river runners, biologists, botanists and climate-change scientists is concerned about. The dust is speeding up the spring snowpack melt by days or weeks. As a result, hydroelectric dams can’t generate power as long. Rafting season ends early. Plants dry up or have shorter pollinating seasons…

They want to learn just how badly the blown dust has sullied the snow surface. To do this, they measure albedo – the amount of solar radiation an object reflects. An albedo of 1.0 means that 100 percent of the sun’s radiation is reflected. If there were no dust, the albedo of spring snow would be about 0.8, Landry says. Last year, the albedo here reached an extremely low 0.35. At that number, snow can absorb double or triple the amount of solar energy as clean snow; it’s not unusual for melt rates to roughly double at low albedos, Landry says. The center’s 11 sites scattered around the Colorado mountains from Rabbit Ears to Wolf Creek all showed low albedos in 2013.

“That’s a gigantic bonus of energy going into the snowpack,” Landry said. “What we’re measuring across Colorado is severe drops in albedo because of dust.”

There’s a common misconception that snowmelt rate is based on air temperature. But it’s much more related to solar-energy absorption, making albedo a crucial factor, Landry emphasizes.

“The conventional wisdom is hard to overcome,” he said.

Senator Beck Basin is the “sentry” study area, the front line for the Colorado Plateau dust as it blows across Colorado…

So much science and data. Who needs it? For starters, the Bureau of Reclamation, the cities of Grand Junction and Denver and water-conservation districts around the state. All are stakeholders that help fund the center. Researchers also take advantage of the data, much of which is accessible at http://www.codos.org.

Ken Curtis, engineer with the Dolores Water Conservancy District, says that although dust has been blowing into Colorado for millennia (Great Sand Dunes is an obvious example), it’s become apparent that since drought years of the early 2000s, dust storms are getting worse. And the dust “does affect how the snow comes off during runoff.”

The immediate data help in knowing how quickly snow will melt, but Curtis says that the bigger value may be in the long-term data. For water managers, big-picture questions loom: Is the dust, indeed, a result of drought? Is it human-caused? Is there a way to control it?[…]

Although “climate change” isn’t a point of emphasis, it’s something that the data might show.

“We know what we’re doing here will contribute to understanding global change,” Landry says.

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