Abstract
Abstract. Ephemeral snowpacks, or those that persist for < 60 continuous days, are challenging to observe and model because snow accumulation and ablation occur during the same season. This has left ephemeral snow understudied, despite its widespread extent. Using 328 site years from the Great Basin, we show that ephemeral snowmelt causes a 70-days-earlier soil moisture response than seasonal snowmelt. In addition, deep soil moisture response was more variable in areas with seasonal snowmelt. To understand Great Basin snow distribution, we used MODIS and Snow Data Assimilation System (SNODAS) data to map snow extent. Estimates of maximum continuous snow cover duration from SNODAS consistently overestimated MODIS observations by >25 days in the lowest (<1500 m) and highest (>2500 m) elevations. During this time period snowpack was highly variable. The maximum seasonal snow cover during water years 2005–2014 was 64 % in 2010 and at a minimum of 24 % in 2014. We found that elevation had a strong control on snow ephemerality, and nearly all snowpacks over 2500 m were seasonal except those on south-facing slopes. Additionally, we 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, physics-based modeling is needed that can account for the complex energetics of shallow snowpacks in complex terrain. These modeling efforts will need to be supported by field observations of mass and energy and linked to finer remote sensing snow products in order to track ephemeral snow dynamics.
Highlights
Seasonal 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)
(1) What are the implications for soil moisture from seasonal to ephemeral snowmelt? (2) How does topography affect snow seasonality? And (3) what mechanisms cause ephemeral snowpacks and how does that vary with climate? We find that ephemeral snow originates from melt and shifts to lower-elevation rain–snow transitions during warm winters, which leads to a fundamentally different soil moisture response than from seasonal snowmelt
We contrast soil moisture response at two adjacent SNOTEL stations that differ in elevation by > 500 m (Fig. 1)
Summary
Seasonal 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). Despite the importance of seasonal snow to water supplies, much of the world’s snow is ephemeral (or intermittent), which means it melts and sublimates throughout the snow cover season instead of having one consistent period of snowmelt. A shift from seasonal to ephemeral snowpacks will have negative implications for the winter tourism that requires continuous snow cover, as well as water management and hy-
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