The dual role of snowfall in impacting surface albedo and spring snowmelt in the Upper Colorado River Basin

Abstract

Abstract Dust has major impacts on snow albedo and snowmelt in the Upper Colorado River Basin (UCRB), which supplies water to much of the western United States. Dust is deposited through both dry (gravity and turbulence) and wet (precipitation scavenging) processes. Wet deposition is harder to detect because dust becomes embedded in falling hydrometeors and buried under fresh snow, only emerging on the snow surface during melt. While dry deposition of dust immediately darkens the snow surface, wet deposition can ultimately contribute more to seasonal dust radiative forcing, despite initially increasing snowpack albedo. Although most snowfall prolongs snowpack, wet deposition snowfall events can paradoxically shorten snowpack duration. Using lower-atmosphere observations from the Surface Atmosphere Integrated Field Laboratory (SAIL) campaign, we find that wet deposition accounts for the majority of dust deposition events in this region (54% in 2022, 86% in 2023). Our SNOBAL model simulations confirm that dust radiative forcing from wet deposition events alone advanced the date of snow disappearance by 14 days in 2023. These results show that infrequent wet deposition events, which constitute less than 15% of snowfall events in the UCRB, can significantly alter snowmelt timing and should be closely monitored by water resource managers.