Spatial Variability of Snow Accumulation and Ablation due to Elevation, Aspect, and Vegetation

Snowpack is a vital water resource in the Intermountain West, where water supply relies on mountain snowmelt which supplies surface runoff and recharges regional groundwater. Climate change is threatening these water resources by decreasing peak snowpack Snow Water Equivalence (SWE), delaying the initiation of snow accumulation, and decreasing the fraction of precipitation falling as snow. Warming during winter and spring results in earlier initiation of snowmelt and slower melt rates which reduce both runoff efficiency and groundwater recharge. These reductions in both streamflow and recharge suggest that a warming climate will result in increased vapor losses either as evaporation or sublimation from the snowpack. Quantifying how spatial heterogeneity in landscape structure differentially influences these vapor fluxes will become increasingly important for predictions of snowmelt-driven water supplies in a warmer future. To address this knowledge gap, we ask 1) What processes control the spatial variability in net snow accumulation before melt? and 2) Is snowpack ablation governed by topographic and vegetation conditions that control spatial patterns in energy balance? We address these questions using long-term observing sites and dispersed snow surveys in Little and Big Cottonwood Canyons, Utah across a range of elevation, aspect, and vegetation structures. Observed 2022 peak SWE at maximum accumulation ranged from 100 cm at the highest elevation (2,793 m) to 24 cm at the lowest elevation (2,224 m). Little Cottonwood Canyon's peak SWE (or net accumulation) was approximately two times Big Cottonwood's peak SWE for any given elevation, highlighting the role of catchment orientation in net SWE input. In both catchments, north-facing sites had on average 20% higher peak SWE values compared to paired south-facing sites suggesting winter vapor losses were related to solar radiation. Both topographic and vegetation shading also delayed melt initiation with shaded environments accumulating snow well past April 1st (average date of peak SWE), for several weeks after melt had begun in higher energy environments. This work contributes to a predictive model of streamflow developed in collaboration with Salt Lake City Department of Public Utilities.