Assistant Professor University of Utah Salt Lake City, Utah, United States
Seasonal mountain snowmelt dominates water resources in the Western USA, providing up to 80% of streamflow in the Colorado River Basin (CRB). Contribution of this snowmelt to streamflow manifests as both surface and subsurface runoff, with fractional contributions varying with snowfall, topography, soils, land use, and vegetation structure. In order to better understand snow water resources, and how they are changing over time, it is critical to understand not only how much water is held as snow, but also when and how fast it will melt and move through the hydrologic system. One important control on snowmelt timing and magnitude is surface darkening from episodic dust deposition, which accelerates snowmelt by lowering snow albedo directly in the visible wavelengths, where snow is most reflective, and indirectly in the near infrared wavelengths due to accelerated snow aging. The impact of dust, quantified as the radiative forcing (RF), is intensified as snow begins to melt because separate dust layers, previously deposited and then buried, combine at the surface to compound surface darkening. In the spring this darkening coincides with increasing day length and higher sun angles, which leads to higher RF and earlier exposure of darker surfaces beneath the snow. The headwaters of the CRB, the Rocky Mountains, are adjacent and upwind from dust emitting arid and disturbed landscapes. In this region, dust radiative forcing has been shown to accelerate snowmelt by 3-5 weeks, reduce total water yield, control timing and magnitude of snowmelt, and correlate with errors in operational snowmelt runoff forecasting. Although dust has been most well studied in the Colorado Rockies, studies also show that dust plays an important role for seasonal mountain snowmelt in other parts of the world, as well. This talk will discuss what we currently know about process and impacts of dust on snow and what the implications are for snow water resources and mountain watersheds.
