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

Abstract

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.