Aspen looks to AGCI data network to support water planning

After a promising winter snowpack, a disappointingly dry spring unfolded into a hot, arid summer in the Roaring Fork Valley this year. Even before the fire broke out at Grizzly Creek, anxieties about low river flows were running high for many municipalities, farmers and ranchers, and recreationalists in the West. Burning under prime fire conditions in dangerous terrain, the Grizzly Creek fire has now grown to be the largest conflagration in the history of White River National Forest. Related concerns about impacts to water supplies are growing as well, as landscapes damaged by fire can lead to erosion that degrades water quality. Meanwhile, the Grizzly Creek fire’s location near the City of Glenwood Springs’ water out-take has led the town to enact watering restrictions and temporarily divert water from the Roaring Fork, which was already experiencing lower than average flows this year.

Water worries are nothing new in the West, but as climate change leads to warmer temperatures, understanding the relationship between climate and water becomes increasingly important. Long-term research can help us better understand and track some of these water/air relationships, and, hopefully, help inform adaptive planning for the future.

AGCI’s ongoing iRON program gathers data across the Roaring Fork Watershed to help answer questions about local climate change impacts. The most recent addition to the iRON sites, a weather and soil moisture station up Castle Creek, was installed in direct response to the City of Aspen’s efforts to gain insight into water and weather dynamics in the Castle Creek basin, a key water supply for the City and downstream users.

The Castle Creek station was installed in 2019 and came online this summer. Funded by the City of Aspen and sited on Pitkin County land, Castle Creek is the most complex station to be added to iRON yet. Other stations in the network measure air temperature, relative humidity, rain, soil temperature (at an 8-inch depth) and soil moisture (at 2-, 8-, and 20-inch depths). The Castle Creek station is additionally equipped to measure wind speed and direction, snow depth, and radiative balance (how much light is reflected off of the ground). The additional sensors give researchers a more nuanced understanding of the water cycle, allowing us to measure how much of the water that falls from the sky as rain or snow ends up in soils or streams vs. how much evaporates back into the atmosphere. Wind speed, for example, is tied to evaporation. On a windy day, more water tends to be lost from soils or plants during respiration. The radiative balance sensor (pyranometer) helps fill gaps in understanding about snowpack: fresh white snow will reflect more light than snow that has partially melted out, revealing darker ground beneath it. Similarly, clean, white snow reflects more light than snow that has been covered in a layer of dust. Being able to track things like a “dust on snow” event in relation to snow depth can illuminate how these dust events may lead to more rapid melting, which in turn has implications for soil moisture and spring water supply more broadly.

It is not possible to predict exactly how climate change will affect water supplies in the West in the coming decades. But through careful observations, we can gain insight into the subtle and diverse ways that the air, soil, snow, and streams interact across our watershed, thereby adding to our toolbox for water management in an uncertain future.