By Mark Esper
“We had a big — and long — winter,” says Chris Landry at the Silverton-based Center for Snow and Avalanche Studies. And not only that, some “sneaky” dust-on-snow events made things tricky for forecasters trying to translate how the snowpack converts into stream flows.
“We had a very delayed onset of spring runoff, with ongoing accumulation of snowpack into April and May — and late May,” Landry said on Monday, June 27. “Then we had another blip of snow a week ago.”
Landry said the snow that continued to pile up in April and into May covered up the fact that the San Juans also got blanketed with layers of dust from the desert Southwest in 11 separate events.
Much of the dust is attributed to man-made disturbance of the “biological crust” in desert regions of the Southwest.
“It was very rarely apparent to people,” Landry said. “It was quickly buried by new snow. It gave us the sense that we didn’t have any dust, when actually we had 11 events.”
Dust on the snow absorbs more energy from the sun and causes the snowpack to dissipate more quickly, up to several weeks earlier than it otherwise would. That in turn has implications for water users downstream who rely on the Rockies as a sort of giant water tower to slowly release its snowpack.
To make things worse, this season’s worst dust event came on May 29, followed by warm weather that caused rapid runoff.
“Water managers hope for a long-duration, low-amplitude snowmelt runoff,” Landry said. “But these events set the stage for exactly the opposite. We went from a clean to a very dirty snow surface overnight with a very large snowpack under it. It guaranteed that runoff would very rapidly accelerate.”
Landry said he notified water managers of the problem.
“We advised water users around the San Juans and the state about this likelihood that snowmelt rates would jump very quickly,” Landry said.
In 2009, heavy dust events advanced the runoff by about five weeks, Landry figures.
“This year we had a whole new twist on things, with a prolonged accumulation of snowpack mixed with dust, then that final capping of dust,” Landry said. “Then the whole snowmelt cycle took off.”
The Center for Snow and Avalanche Studies monitors dust deposits on snow at 11 sites in the state.
“It was a tense and challenging runoff season for a lot of agencies and emergency managers,” Landry said. “We’re trying to cope with a delayed snowmelt season and the effects of dust in amplifying the rate of melt. And only at the end did it become obvious.
“It was sneaky in that way this season.”