A multi-decadal climatology of dust-on-snow from wet deposition in the Upper Colorado River Basin

Abstract. Dust-on-snow deposition is the dominant factor in earlier snowmelt timing in the Upper Colorado River Basin (UCRB), which gets ~70 % of its annual streamflow from snowmelt. Previous studies have demonstrated the radiative effects of dust-on-snow deposition, but have not quantified what deposition types, whether from atmospheric turbulence (dry deposition) or hydrometeor scavenging (wet deposition), drive these radiative effects. Here, we produce a climatology of the total amount and type of dust-on-snow deposition in the UCRB using the Modern-Era Retrospective analysis for Research and Applications (MERRA-2) reanalysis dataset from 1980–2023 and evaluate its accuracy using Surface Atmosphere Integrated Laboratory (SAIL) field measurements taken in 2022 and 2023 and Moderate Resolution Imaging Spectrometer (MODIS) Snow Property Inversion from Remote Sensing (SPIReS) dust concentration data. The results show that wet deposition is the dominant form of dust-on-snow deposition in the UCRB, comprising 73.8 % of total dust deposition. Additionally, the eastern areas in the UCRB, particularly the Gunnison Watershed, experience 16 % higher wet deposition monthly totals (69.33 mg m^-2) than the entire UCRB average (59.80 mg m^-2). These results highlight the importance of persistent spatial patterns but also interannual variability in accounting for dust deposition. This climatology also contextualizes the long-term records of dust deposition by showing how the relationships between dust at several sites with decadal records project onto the entire Basin, while also supporting water resource planning, especially for areas with elevated wet deposition levels.