Inter- and Intra-Annual Variability in Snow Albedo, Grain Size, and Snow Covered Area from the Airborne Snow Observatory during Low Snow Years (2013-2015)

The Sierra Nevada snowpack is critical to the state of California, and the consistently lower than average snowfall during the dry winters of 2012-2015 contributed to statewide water stress. These ‘snow drought’ years could become more frequent in a warmer future; therefore it is of interest to understand spatial and temporal trends in snow properties during low snow years. Here we assess inter- and intra-annual variability in snow-covered area, snow albedo, grain size, and impurity radiative forcing across three low snow years in the Tuolumne River Basin above Hetch Hetchy Reservoir. Snow properties retrievals are made by the Airborne Snow Observatory (ASO), a coupled imaging spectrometer and lidar platform, which has been measuring spatial and temporal distribution of both snow water equivalent and snow albedo across key basins in the Western US since 2013. It is generally understood that net solar radiation (as controlled by variations in snow albedo and irradiance) provides the energy available for melt in almost all snow-covered environments, yet there are no spaceborne sensors that can adequately capture trends in this critical snow property at relevant spectral, spatial, and temporal scales in mountainous terrain. This data set offers the unprecedented opportunity to improve our understanding of what controls snow albedo in mountain basins, and its relationship with spatial and temporal snowmelt patterns.  (KEYWORDS:  remote sensing, snow hydrology, snow albedo, snow grain size, Airborne Snow Observatory)