Soil-moisture monitoring station in Roaring Fork Valley completes local water-research network
Castle Creek site provides insights for researchers and water managers seeking to understand Colorado River watershed conditions
Last summer, the Aspen Global Change Institute’s first subalpine soil-moisture and snowpack-monitoring station began transmitting live data to researchers, stakeholders and the Aspen water department.
The station, which sits at 11,500 feet on Cooper Basin Road near the edge of the Castle Creek watershed, tracks soil moisture at multiple depths; soil temperature; snow depth; wind speed and direction; air temperature; humidity; and radiative balance. That data is made available online in real time.
“The new station fills a gap in that there wasn’t information being measured at that elevation,” AGCI research director Julie Vano said recently.
AGCI now has 10 stations covering the major elevation zones and ecosystems present in the Roaring Fork Valley.
The stations, known as the Interactive Roaring Fork Observation Network (iRON), gather data on soil-moisture levels, which are key but understudied variables in streamflow forecasting. In the 2020 Western Water Assessment report for the Colorado River upper and lower basins, scientists emphasized that surface soil-moisture data — critical for streamflow forecasting and for monitoring the impacts of climate change on the hydrologic cycle — was sparse.
Gathering data at all elevations throughout the Roaring Fork Valley provides scientists with a localized, clearer picture of how climate change is impacting the hydrologic cycle at the Colorado basin’s headwaters. The study of headwater areas is important because 15% of the upper and lower basins’ surface area — primarily the high mountains of the Western Slope, but also spanning mountainous areas in Utah and Wyoming — provides 85% of total annual runoff into the Colorado River.
A storehouse of data
The AGCI network gives scientists the opportunity to study how elevation and varying ecosystems shape soil-moisture retention.
“People who live in the mountains know that everything varies a lot in a pretty small geographic distance,” said ACGI community science manager Elise Osenga. “You’ll have changes in soil type, changes in plants, even changes in rainfall from one mile to the next mile over.”
As the network continues to accumulate data, it will create a local picture of climate change’s impacts on the water cycle. Throughout the upper basin, scientists have shown that snowmelt and runoff are occurring earlier than they did between 1950 and 2000. Every degree of warming is expected to reduce upper-basin runoff by between 2-6%. Having a data record for a specific basin will give these impacts a local focus, Vano said.
Since 2015, AGCI staffers have been submitting their data to international hydrologic and soil-moisture databases.
“Since we started sharing, over 1,800 requests for our data have been made,” Osenga said.
The ACGI is working to create partnerships with other soil-moisture monitoring basins and research institutions across the West to share data, allowing for future hydrologic studies involving intrabasin comparisons.
“Nothing is fully underway just yet,” Osenga said.
Determining climate-change trends via iRON data will take time to develop. The first iRON station was created in 2012. Of the 10, six have been installed since 2015. As the length of the record grows, it will become increasingly easier to detect climate change trends, Vano said.
Adding to the uncertainty, the Colorado River basin has been in an extended dry period marked by frequent droughts since 2000, marking “the driest 21-year period in the Colorado River asin in more than 100 years of record keeping and one of the driest in the past 1,200,” according to a 2021 U.S. Bureau of Reclamation report on water-supply security.
“We have really short data records, and those data records exist within an already really dry period,” Osenga said of iRON.
So, in order to gain an understanding of soil moisture in the Roaring Fork Valley, data from future potentially droughtless years is needed, Osenga said.
While drought is predicted to become more frequent and intense in the future, it is less clear how precipitation trends — which are the greatest drivers of soil moisture — will take shape. Some models indicate that precipitation could increase in the upper basin in the coming decade, which would reshape iRON’s soil-moisture data, Osenga said.
Don’t be so predictable
While long-term trends from the Roaring Fork data remain ambiguous, yearly data provides useful insights for the Aspen water department in predicting spring- and summer-streamflow conditions.
“When I’m not in meetings and other obligations, I’m constantly looking at data,” said Steve Hunter, utilities resource manager for the city of Aspen.
To better predict spring streamflow, Hunter checks weather and snowpack data from national organizations such as the U.S. Geological Service and the National Resource Conservation Service. Hunter frequently checks data from the NRCS Snow Telemetry (SNOTEL) sites in the Roaring Fork watershed. The SNOTEL site at Independence Pass is closest to Castle Creek, which provides the majority of Aspen’s water, Hunter said. On Wednesday, the snow-water equivalent measured at Independence Pass was at 13.8 inches, which is 91% of average, calculated from data from 1981 to 2010. Snow depth, which is different from SWE, at Independence Pass was at 52 inches. At the Castle Creek iRON station, snow depth was at 53 inches.
Hunter also tracks the information coming from iRON. Soil-moisture data ends in the fall, when frozen water begins accumulating on the soil as snow. In the fall of 2020, seven of nine stations had the lowest levels of soil moisture on iRON station record, said Osenga. (The Castle Creek iRON station was not included in analysis.) Of the two with higher water levels than prior years, one station is in an irrigated area, providing an artificial boost to moisture levels, Osenga said.
Dry fall soil conditions mean that as snow begins to melt this spring, more water will soak in — and be absorbed by plants and the atmosphere — before running into local creeks and rivers, Osenga said.
Hunter is holding out hope that more stormy weather could give the snowpack the boost it needs for adequate streamflow this spring and summer.
“We’re just hoping we get a lot of snow and then liquid precipitation in the spring,” said Hunter.
Deciding what’s important
While the AGCI plans on expanding its reach through collaborations, the organization does not plan to add more iRON sites in the near future. Each site has been funded by a combination of partners, including private organizations, government entities and educational interests.
“It’s supported by the community, which is really amazing,” Vano said of iRON. “You don’t see that often in the world of science. So, the community is really deciding that understanding these changes is really important.”
Aspen Journalism is a local, nonprofit, investigative organization covering the environment in collaboration with The Aspen Times and other Swift Communications newspapers. For more, go to http://www.aspenjournalism.org.
Editor’s note: This story was updated from its initial version to correct its characterization of predictions about climate change’s impact on streamflow, as well as AGCI’s expectations about how long it will take for data from iRON stations to show evidence of climate change.
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