Despite the importance of mountain snowpack to understanding the water and energy cycles in North America, global snow storage estimates are highly uncertain, particularly for mountain regions. 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. Thus, the role of snow in the hydrologic cycle at continental scales has never been adequately quantified. Advances in regional models, however, show promise in estimating snow water equivalent in mountains. Not only do regional models have higher spatial resolution, which allows for more realistic simulation of orographic processes, but they also include feedbacks between the snow surface and the atmosphere.
Here we use the Weather Research and Forecasting (WRF) regional model, at 9-km resolution, to simulate snow accumulation across the mountainous regions of the North American continent. Additionally, we develop a novel technique to create a "representative climatology" instead of the traditional 30-yr climatology. That is, we estimate a single average snow accumulation year for each individual mountain range, rather than a continuous multiyear simulation over the entire continent. Our new method decreases the amount of computational time necessary to complete all simulations.
From our WRF simulations, the climatological peak snow-water storage (SWS) in North American mountains is 1,010 [km.sup.3], 2.95 times larger than previous estimates. By combining this mountain SWS value with the best available global product in lowland areas, we estimate peak North America SWS of 1,687 [km.sup.3], 55% greater than previous estimates. Though mountains comprise 25% of the continental 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 31% of the total continental SWS accumulating in mountains. Our results show that the importance of snow in the North American water budget may have been underestimated.
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. Model and observational methods must continue to be adapted for mountain regions in order to quantify the large-scale water cycle.--MELISSA L. WRZESIEN (THE OHIO STATE UNIVERSITY), M. T. DURAND, T. M. PAVELSKY, AND S. KAPNICK, "A new estimate of North American mountain snow accumulation from regional climate model simulations," presented at the 32nd Conference on Hydrology, 7-11 January 2018, Austin, Texas.
Caption: Improved Snow Water Estimates. Peak snow water equivalent composite for mountain areas in North America from separate representative-year WRF simulations for each range. Tan areas indicate glaciers, for which WRF snow water equivalent values are not reported.