A New Estimate of North American Mountain Snow Accumulation from Regional Climate Model Simulations

Despite the importance of mountain snowpack to understanding the water and energy cycles in North America’s montane regions, no reliable mountain snow climatology exists for the entire continent. In situ networks are too sparse in complex mountain environments, remotely sensed retrievals have high uncertainty in deep snowpacks, and global models are thought to underestimate mountain snow accumulation. We present a new estimate of mountain snow water equivalent for North America from regional climate model simulations run at 9 km resolution. For the regional climate simulations, we develop a new technique to create a “representative climatology” instead of the traditional 30-year climatology. Here we use the Weather Research and Forecasting (WRF) model to simulate average snow accumulation years for individual mountain ranges, rather than a continuous many year simulation over the entire continent. Our new method decreases the amount of computational time necessary to complete all simulations. After stitching the WRF simulations together, the climatological peak snow water storage (SWS) in North American mountains is 1010 km³, 2.95 times larger than previous estimates from reanalyses. By combining this mountain SWE value with the best available global product in non-mountain areas (here we use the ensemble product CanSISE), we estimate peak North America SWS of 1687 km³, 55% greater than previous estimates. In our simulations, the date of maximum SWS varies widely by mountain range, from early March to mid-April. Though mountains comprise 20% of the continent’s land area, we estimate that they contain ~60% of North American SWS, suggesting that mountains hold a disproportionate amount of snow storage compared to the rest of the continent. Previous estimates have far less snow in mountain regions, with only ~30% of the total continental SWS accumulating in mountains. This new estimate is a suitable benchmark for continental- and global-scale water and energy budget studies. In addition, the results presented here suggest that mountain snow is a significant part of the continental water cycle, highlighting the need for better mountain representation in modeling.