Snowmelt‐Radiation Feedback Impact on Western U.S. Streamflow

• Published in: Geophysical research letters Vol. 50; no. 23
• Main Authors: Ban, Zhaoxin, Xin, Chen, Fang, Yiwen, Ma, Xiaoyu, Li, Dongyue, Lettenmaier, Dennis P.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.12.2023; Wiley
• Subjects: Albedo; Annual runoff; Basins; climate warming; Coefficients; Evapotranspiration; Feedback; Global warming; Headwaters; High temperature; Hydrologic models; Mountains; Radiation; Radiation absorption; Regional climates; River basins; Rivers; Runoff; Runoff coefficient; Runoff decrease; runoff sensitivity; Sensitivity; Snow; Snow cover; Snowmelt; snowmelt‐radiation feedback; Solar radiation; Solar radiation absorption; Stream discharge; Stream flow; water resources; western U.S; Winter temperatures; Western states; United States > US; Colorado River
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL105118

Ongoing runoff declines in the Colorado River Basin have been shown to be predominately driven by decreasing albedo from warming‐driven snow‐cover loss, especially in late‐spring (hereafter snowmelt‐radiation feedback). Here, we explore the feedback's impact on annual runoff sensitivity to warming across the western U.S. (WUS) using hydrologic model simulations. For 1°C uniform warming, we show that runoff is most sensitive to warming in modestly snow‐covered, interior mountain headwaters, especially the Rocky Mountains. Runoff sensitivities are most associated with the snowmelt‐radiation feedback in basins with runoff coefficients between 0.2 and 0.6, where runoff sensitivity increases with more snow and lower winter temperature. In aggregate, ∼48% of WUS runoff sensitivity is attributable to the snowmelt‐radiation feedback and is especially pronounced in the warming‐sensitive river basins (annual runoff decreases >5%/°C). We also show that the feedback's impact decreases with increasing temperature, which has unresolved implications for streamflow declines in a less‐snow future. Plain Language Summary Regional climate warming is driving strong runoff changes in the western U.S. (WUS), especially the Upper Colorado River Basin (UCRB). Previous work showed that warming‐related snow cover reductions lead to more solar radiation absorption and evapotranspiration, which largely explain ongoing runoff declines in UCRB. Here, we assess the impact of this snowmelt‐radiation feedback on warming‐induced runoff changes across WUS. In a warmer world, we find that the largest annual runoff sensitivities are in the interior mountainous WUS with modest snow cover. The snowmelt‐radiation feedback explains over half of the warming‐induced runoff changes in warming‐sensitive WUS basins and about half of WUS' overall runoff sensitivity. In areas influenced by the snowmelt‐radiation feedback, both runoff sensitivity and the feedback's contribution become smaller with higher temperatures, suggesting a potentially slower rate of streamflow decline as temperatures rise in a warmer future. Key Points Snowmelt‐radiation feedback accounts for ∼1/2 of warming‐driven runoff decline across the Western U.S. (WUS) Runoff sensitivities are most linked to snowmelt‐radiation feedback in river basins with runoff coefficients in the range 0.2–0.6 Runoff sensitivities to warming are largest in modestly snow‐covered, interior mountainous parts of WUS, especially the Rocky Mountains