How much of Aspen’s snowpack will make it to the rivers? Soil moisture holds a key
Warm temperatures and dry winds took a big bite out of a snowpack that was sitting pretty just 10 days ago but now is at risk of disappearing ahead of schedule.
That creates the potential to create an early peak runoff for rivers and leave the mountains surrounding Aspen high and dry later in the summer.
The snowpack was 103% of median at the headwaters of the Roaring Fork River east of Aspen on April 30. By May 7, it dropped to 81%, according to the U.S. Natural Resources Conservation Service’s automated snow telemetry site.
The Aspen Global Change Institute is keeping a close eye on conditions with 10 field stations placed strategically around the mainstream of the Roaring Fork. Unlike the Snotel sites, the institute’s stations monitor soil moisture at 2, 8 and 20 inches below the surface.
Soil moisture isn’t often used for modeling in hydrology, but it can play a big role in how much of the Elk Mountain snowpack makes it to the rivers and streams — and ultimately to irrigation ditches and fields.
“It can help us determine how much of the snow is going to turn into streamflow,” said Elise Osenga, community science manager for Aspen Global Change Institute. “Snowpack absolutely matters, but it’s not the only thing that matters.”
For example, an abnormally warm and dry late winter and spring 2018 resulted in the snowpack melting out three weeks earlier than 2013-17, Osenga said. 2013 is the first year that the climate stations were operating so historical data is limited.
During the 2018-19 winter, snowpack was cruising along at about average until the snow spigot was turned on in early March and continued well into April. The snowpack melted out later than average, hanging on into July in higher elevations. That created high soil moisture levels generally around the valley, but dry conditions during the summer and into fall depleted the levels heading into winter.
AGCI researchers will watch how that lower soil moisture affects runoff from this spring’s snowpack and the resulting streamflow levels. The more water absorbed by the dry ground, the less that makes it to rivers and streams.
The field stations range from 6,200 feet near Glenwood Springs to 12,080 feet near the summit of Independence Pass. Two stations were placed in Northstar Nature Preserve, with its special ecosystem that includes aspen groves and meadows.
Collectively, the field stations are known as the Interactive Roaring Fork Observation Network or iRON.
Osenga said the field stations came about as part of a collective community concern. Officials with the city of Aspen and Pitkin County are concerned about how climate change could affect the forests in the upper Roaring Fork Valley. AGCI is helping them by tracking soil moisture as well as soil and air temperatures and precipitation.
“The long-term goal really is a community-driven goal,” said
Data from most of the sites is collected every 20 minutes and transmitted every four hours.
If there is a change of the health of the Aspen area’s forests, Osenga said, AGCI and its partners will be able to look at the field of data and analyze what happened and when. It’s like tracking an on-going mystery, she said.
“That’s the kind of goal that will take a couple of decades to determine because we’re looking for trends,” Osenga said.
The Independence Pass station was added in 2016 and will provide data on how climate change is affecting the highest elevations.
“We knew we wanted something 12,000 feet or higher,” Osenga said.
Another nonprofit organization, Independence Pass Foundation, helped fund the station, which was placed on a mining claim held by Pitkin County. The station looks like an old TV antenna sticking out of ground covered in alpine willows just west of the summit. The site gets blasted by wind, buried by snow and threatened by lightning strikes.
“It’s a tricky site. It’s really exposed,” Osenga said.
The station stopped transmitting data via satellite April 24, so Independence Pass Foundation executive director Karin Teague skied up to it from Upper Lost Man on Tuesday to hit the reset button. Unfortunately, it didn’t take. Osenga said the system will automatically reset in a few more days and hopefully transmit the data it stored.
The site is particularly valuable because it is the only station in iRON that measures snow depth. As of April 24, it measured 61 inches.
Soil moisture and temperatures at Independence Pass will be closely monitored to see if higher temperatures and lower moisture leads to a change in the type of plants growing there. A warming climate could endanger vegetation at the highest climates.
“They don’t have somewhere else to move up to,” Osenga said.
AGCI also tracks the types of plants, and when plants bloom on a 100-square-meter plot of ground on Independence Pass.
As with the entire iRON network, the data is not only designed to provide data long-term to researchers but also provide real-time useful information to public land managers and water managers, particularly through soil moisture levels.
“What’s that mean for ecology and water supplies?” Osenga said.
More on AGCI’s field stations and the data can be found at https://www.agci.org/iron/stations.
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