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Coordinated observations in the Upper Colorado River Basin support improved prediction of water resources from mountainous regions

An X-band precipitation radar (XSAPR) is pictured on Crested Butte Mountain in Colorado as part of the SAIL (Surface Atmosphere Integrated Field Laboratory) campaign. Source: image courtesy of the DOE Atmospheric Radiation Measurement (ARM) user facility.

Mountains are vital headwaters to many rivers, supplying a significant amount of the freshwater used by the Earth’s population. Predicting water supply in mountainous regions is especially challenging due to their complex terrain, and continued climate changes are expected to significantly impact water availability for millions of people. The Colorado River Basin, a primary source of water for much of the southwestern United States, is estimated to see reductions in runoff ranging between 10% to nearly 50% by mid-century, raising concerns about its long-term reliability as a critical water source. Snowmelt in the Rocky Mountain headwater region is the primary contributor of annual streamflow and water reservoir storage in the basin, but surface observing systems in the region are limited, and existing systems do not capture important land and atmospheric variables at fine enough scales to accurately predict the timing and availability of water resources. 

To help improve understanding and prediction of water availability in the region, a suite of observational campaigns in the East River Watershed of the Upper Colorado River Basin is collecting detailed measurements of atmospheric and land–atmosphere interaction processes that impact mountain hydrology and runoff into the basin. The DOE-led SAIL (Surface Atmosphere Integrated Field Laboratory) and the NOAA-led SPLASH (Study of Precipitation, the Lower Atmosphere and Surface for Hydrometeorology) field campaigns coordinated a network of state-of-the-art observational sites from fall 2021 through summer 2023 in a remote headwater region in the Colorado Rocky Mountains. These atmospheric-focused observations were coordinated with long-term DOE research activities focusing on the terrestrial and hydrological processes of the watershed. Measurements include near-surface air temperature, cloud properties, precipitation amount, soil moisture, surface heat flux, snow depth, and complex interactions between the surface and lower atmosphere that help to regulate evaporation of surface moisture and snow. Additional observations focusing on snowpack properties were supported by NSF. 

Initial results include analyses of a series of wintertime precipitation events that impacted the region in winter 2021-2022, including an extreme snowfall event in late December 2021; studies of aerosol properties and impact on precipitation and snow reflectivity; and the role of the North American monsoon on warm season precipitation. In addition, results include evaluation of a model’s ability to capture the impact of changes in the Earth's surface energy balance during the seasonal snow cover transition on the vertical structure and circulation of the lower atmosphere. Ultimately, these advances will contribute to improving prediction capabilities of weather models and Earth System Models in complex terrain.