The shrinking Great Salt Lake contributes to record high dust-on-snow deposition in the Wasatch Mountains during the 2022 snowmelt season

Abstract

Seasonal snowmelt from the Wasatch Mountains of northern Utah, USA is a primary control on water availability for the metropolitan Wasatch Front, surrounding agricultural valleys, and the Great Salt Lake (GSL). Prolonged drought, increased evaporation due to warming temperatures, and sustained agricultural and domestic water consumption have caused GSL water levels to reach record low stands in 2021 and 2022, resulting in increased exposure of dry lakebed sediment. When dust emitted from the GSL dry lakebed is deposited on the adjacent Wasatch snowpack, the snow is darkened, and snowmelt is accelerated. Regular observations of dust-on-snow (DOS) began in the Wasatch Mountains in 2009, and the 2022 season was notable for both having the most dust deposition events and the highest snowpack dust concentrations. To understand if record high DOS concentrations were linked to record low GSL levels, dust source regions for each dust event were identified through a backward trajectory model analysis combined with aerosol measurements and field observations. Backward trajectories indicated that the exposed lakebed of the GSL likely contributed 23% of total dust deposition and had the highest dust emissions per surface area. The other potential primary contributors were the Great Salt Lake Desert (45%) and the Sevier + Tule dry lakebeds (17%), both with lower per-area emissions. The impact on snowmelt, quantified by mass and energy balance modeling in the presence and absence of snow darkening by dust, was over two weeks (17 days) earlier. The impact of dust on snowmelt could have been more dramatic if the spring had been drier, but frequent snowfall buried dust layers, delaying dust-accelerated snowmelt later into the melt season.

Spatio-temporal patterns and trends in MODIS-retrieved radiative forcing by snow impurities over the Western US from 2001 to 2022

“…We find elevated RF in the San Juan and Parks ranges of Colorado, the first high-altitude contact area for predominantly southwesterly winds transporting dust from the southern Colorado Plateau (Skiles et al 2015). Major dust-on-snow impacts have also been reported in western areas of the Upper Colorado basin, such as in the Utah Wasatch mountains (Lang et al 2023), which are also shown in the analyzed MODIS data (figure 2).…”