Streamflow forecast down for Roaring Fork despite above-normal snowpack — @AspenJournalism #ColoradoRiver #COriver #aridification

The Roaring Fork River (left) joins with the Colorado River in downtown Glenwood Springs. Snowpack in the Roaring Fork basin is slight above normal, but April streamflows are predicted to be just 85% of normal. Photo credit: Heather Sackett/Aspen Journalism

From Aspen Journalism (Heather Sackett):

Although snowpack in the mountains near Aspen is hovering above normal for this time of year, streamflows in the Roaring Fork River are predicted to be just 85% of normal for April.

The snow-telemetry, or SNOTEL, site at Independence Pass, near the headwaters of the Roaring Fork River, is at 106% of normal snow-water equivalent. The SNOTEL site at Kiln, near the headwaters of the Fryingpan River, is at 106% of normal. And at Scofield Pass, home to the headwaters of the Crystal River, the SNOTEL site shows snowpack at 90% of normal. The Roaring Fork basin as a whole is at 112% of normal snowpack.

But the April water-supply outlook released by the National Resources Conservation Service predicts streamflows at just 85% of normal at the confluence of the Roaring Fork and Colorado rivers in Glenwood Springs.

“It’s kind of an anomalous year,” said Karl Wetlaufer, a hydrologist with NRCS and assistant supervisor with the Colorado Snow Survey. “More commonly, the streamflow forecasts do pair with the snowpack pretty well.”

Colorado Drought Monitor April 14, 2020.

The reason for the discrepancy is dry soils, which soak up spring snowmelt before it gets to streams. According to the U.S. Drought Monitor, abnormally dry conditions crept back into Pitkin County in mid-September. By Oct. 22, the western half of the county was in severe drought, while the eastern half was in moderate drought. The western half of Pitkin County is still experiencing either abnormally dry conditions or moderate drought.

“All of late summer was really dry, but before the snow started to accumulate, it was extremely dry,” Wetlaufer said. “The soil can be like a really dry sponge right now and soak up more runoff than usual.”

That lower-than-normal runoff could have impacts on the city of Aspen, which takes its municipal water supply directly from Castle and Maroon creeks. Tyler Christoff, director of Aspen’s utilities department, said city staff is constantly monitoring the variables in the watershed — U.S. Geological Survey gauges, SNOTEL sites, weather forecasts, Drought Monitor — but so far, they are treating this as an average year.

“Being close to average, we are going to let it play out and see if there’s any action we need to take,” Christoff said. “I think regardless of the year and the season, it’s important for our community to be conscious of our use of water as a resource; we do not have an unlimited supply.”

The Colorado River basin typically reaches its peak snowpack for the year in early to mid-April.
NRCS has two main ways of measuring snowpack, which feed into the water-supply forecasts. The first is through SNOTEL sites, which are an automated system of sensors that collect weather and climate data hourly from 115 areas around Colorado, mostly in remote, mountainous watersheds between 9,000 and 11,000 feet. They measure snow depth, water content of the snow, precipitation and air temperature.

Karl Wetlaufer (NRCS), explaining the use of a Federal Snow Sampler, SnowEx, February 17, 2017.

The other way is through snow courses, which are manual measurements of snow depth and water content.

But due to the COVID-19 crisis, NRCS staff did not conduct end-of-March manual snow surveys. Wetlaufer said the agency wanted to follow social-distancing guidelines and not have employees traveling in the same vehicle to remote mountain communities.

“We need to go out in pairs for backcountry work,” he said. “We have been talking about options for next month. Some sites that are key, maybe we can still go out and drive two vehicles.”

But streamflow forecasts for the Colorado River basin barely use any snow-course data, Wetlaufer said, so those forecasts should still be accurate without the manually collected data.

“In the Colorado River basin, there’s really pretty minimal impact,” he said.

Aspen Journalism collaborates with The Aspen Times and other Swift Communications newspapers on coverage of water and rivers. This story ran in the April 13 edition of The Aspen Times.

Map of the Roaring Fork River drainage basin in western Colorado, USA. Made using USGS data. By Shannon1 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=69290878

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