RECENT SHRINKING OF THE GREAT SALT LAKE CONTRIBUTES TO RECORD BREAKING DUST-ON-SNOW DEPOSITION AND SNOWMELT ACCELERATION ACROSS NORTHERN UTAH'S MOUNTAINS (Invited Presentation)

Seasonal snowmelt from mountainous terrain in northern Utah is the principal water source for the metropolitan Wasatch Front, surrounding agriculture, and the terminal Great Salt Lake (GSL). Sustained water consumption coupled with prolonged drought and increased evaporation from warming temperatures have resulted in record GSL low stands in 2021 and 2022. This decrease in lake level has exposed large areas of dry lakebed sediment. During springtime frontal passages, dust is frequently emitted from playas in the eastern Great Basin, including the GSL lakebed, and deposited on the adjacent snowpack of the Wasatch Mountains where the snow is darkened, and snowmelt is accelerated. The 2022 and 2023 seasons were notable for having frequent dust events and high dust-on-snow deposition. Following record-breaking dust deposition in the spring of 2022, source regions for each dust event were identified through a backward trajectory model analysis combined with aerosol measurements and field observations over the 2022 snowmelt season. Our analysis revealed that dust emissions were dominated by sources across Utah’s west desert (~63%) and the GSL lakebed (~23%). Using continuous in-situ measurements at a point scale, snowmelt was simulated through melting in the presence and absence of snow darkening by dust, revealing that dust caused the snowpack to melt 17 days earlier compared to clean snow conditions. To estimate the impacts of dust on snowmelt across the watersheds of the GSL basin, the additional amount of energy absorbed into the snowpack due to snow darkening by dust was quantified using daily MODIS dust radiative forcing retrievals. These retrievals were cross-referenced with a variety of field observations and modeling outputs and brought into context of the 24-year MODIS record (2000-2023). Preliminary results reveal that seasonal meteorology, in addition to the quantity of deposited dust, may have a large control on basin-averaged dust radiative forcing across northern Utah’s snowpack. If high dust deposition continues and spring weather trends drier, we can expect the snowmelt regime to shift - altering watershed fluxes and adding complexities for streamflow forecasters.