Now You See It Now You Don’t: A Case Study of Ephemeral Snowpacks in the Great Basin U.S.A.

Abstract

Ephemeral snowpacks, or those that routinely experience accumulation and ablation at the same time and persist for <60 days, are challenging to observe and model. Using 328 site years from the Great Basin, we show that ephemeral snowmelt delivers water earlier than seasonal snowmelt. For example, we found that day of peak soil moisture preceded day of last snowmelt in the Great Basin by 79 days for shallow soil moisture in ephemeral snowmelt compared to 5 days for seasonal snowmelt. To 5 understand Great Basin snow distribution, we used moderate resolution imaging spectroradiometer (MODIS) and Snow Data Assimilation System (SNODAS) data from water years 2005-2014 to map snow extent. During this time period snowpack was highly variable. The maximum seasonal snow cover was 64 % in 2010 and the minimum was 24 % in 2014. We found that elevation had a strong control on snow ephemerality, and nearly all snowpacks over 2500 m were seasonal. Snowpacks were more likely to be ephemeral on south facing slopes than north facing slopes at elevations above 2500 m. Additionally, we 10 used SNODAS-derived estimates of solid and liquid precipitation, melt, sublimation, and blowing snow sublimation to define snow ephemerality mechanisms. In warm years, the Great Basin shifts to ephemerally dominant as the rain-snow transition increases in elevation. Given that snow ephemerality is expected to increase as a consequence of climate change, we put forward several challenges and recommendations to bolster physics based modeling of ephemeral snow such as better metrics for snow ephemerality and more ground-based observations. 15 IntroductionSeasonal snowmelt supplies water to one-sixth of the world's population, which supports one-fourth of the global economy (Barnett et al., 2005;Sturm et al., 2017). Seasonal snowpack provides predictable melt timing and volumes in the spring, which influences streamflow timing, surface water and groundwater availability (Berghuijs et al., 2014;Jasechko et al., 2014;Stewart et al., 2005). Reliable spring snowmelt also provides a strong control on vegetation phenology and productivity in many 20 ecosystems (Parida and Buermann, 2014;Trujillo et al., 2012). Despite the importance of seasonal snow to water supplies, much of the world's snow is ephemeral, which means it melts and sublimates throughout the snow cover season instead of having one consistent period of snowmelt. Even small shifts from seasonal to ephemeral snowpack due to regional warming could disrupt 1 Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-749 Manuscript under review for journal Hydrol. Earth Syst. Sci. Discussion started: 8 January 2018 c Author(s) 2018. CC BY 4.0 License. snowmelt timing in ways that could alter summer productivity, soil temperature, and soil moisture regimes Harpold and Molotch, 2015;Jefferson, 2011;Parida and Buermann, 2014;Regonda et al., 2005;Stielstra et al., 2015;Trujillo et al., 2012). A shift from seasonal to ephemeral snowpacks will also have negative implications for the wi...

Subsurface Lateral Flows Buffer Riparian Water Stress Against Snow Drought

“…The site was selected as representative of a mid‐elevation, mid‐latitude site due to its availability of multiple, co‐located, and long‐term data sets, such as precipitation, air temperature, snow depth, and streamflow. A complete, quality‐controlled, and gap‐filled record of meteorological data has been made available and covers the period between 1966 and 2018 (Petersky & Harpold, 2018). This data is used to force our ecohydrological model and is described in Text S1 in Supporting Information .…”