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

Seasonal snowmelt from the Wasatch Mountains of northern Utah 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 from warming temperatures, and sustained agricultural and domestic water consumption has led to record-setting declines in GSL levels and 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 in 2009, and the 2022 season was notable for both having the most dust deposition events and most dust deposited. To understand if record high DOS concentrations were linked to record low GSL levels, dust source regions for each dust event were identified through backward trajectory model analysis combined with aerosol measurements and field observations. Modeling indicated that the exposed lakebed of the GSL contributed 23% of total dust deposition and had the highest dust emissions per surface area. The other primary contributors were the Great Salt Lake Desert (45%) and the Sevier + Tule dry lakebeds (17%), with dust lower intensity emissions over larger areas. The impact on snowmelt, quantified by simulating melting in the presence and absence of snow darkening by dust, was over two weeks (17 days) earlier. This impact could have been more dramatic if the spring had been drier, but frequent snowfall buried dust layers and delayed the timing of snow darkening until late in the melt season.