Sensitivity of the snowcover energetics in a mountain basin to variations in climate

Abstract

Abstract:Snow is an important natural reservoir that holds water on the landscape for release later in the season in western North America and other portions of the world. As air temperature increases with global climate change, the character of the generally established seasonal snowcover will be affected. To study the specific response to variable climate, a carefully collected and processed meteorological data set for the 1984-2008 water years (WYs) was assembled for a snow-dominated headwater mountain catchment. The data were used to force a physically based, distributed energy balance snow model to simulate patterns of snow deposition and melt over the catchment for the 25-year period. This period covers both the highest (1984) and lowest (1992) snow seasons on record and exhibits extreme inter-annual variability. This unique forcing data set captured meteorological conditions that resulted in the range of variability in snowcover accumulation, timing of ablation, and the timing and amount of surface water input (SWI), and discharge during the 25-year study period. SWI is the amount of liquid water delivered to the soil surface from melting snow or from rain that passes through the snowcover or falls directly on the soil. Warm winters, characterized by early-and mid-winter rain, triggered earlier inputs from SWI and response in discharge than cool winters. Cool conditions prolonged the generation of SWI and streamflow out of the basin. Very wet conditions that were warm passed 50% of the SWI 27 days earlier and passed 50% of the discharge 15 days earlier, when compared to very wet conditions that were cool. Warmer conditions produced less snow water equivalent, shortened the melt season, and would be expected to extend the summer drought.

Evaluation of distributed hydrologic impacts of temperature-index and energy-based snow models

“…The model is driven by meteorological forcing inputs of precipitation, air temperature, incoming shortwave and longwave radiation, wind speed and relative humidity. Forcing data are distributed across the landscape [27,28,30,34]. The model computes water vapor exchange (sublimation or condensation) between snow and atmosphere, and solves for the temperature and snow water equivalent for each layer at each time step.…”

“…Twenty-five year (1984-2008) basin average water year (WY) precipitation and outflow from the RME watershed are 849 and 505 mm [34]. Over that period, 70% of precipitation fell as snow.…”

“…The RME catchment contains two primary climate stations [32,34]: the Reynolds Mountain climate station (elevation 2097 m), located on a broad shelf at the southwestern edge of the basin, and the Reynolds Mountain snow pillow site (elevation 2061 m), located within a forest opening (Fig. 1).…”

“…1). Solar and thermal radiation, air temperature, humidity, wind speed and direction, and soil temperature are measured at both sites [34,44]. Site-measured values for all parameters are distributed over the watershed.…”

“…Site-measured values for all parameters are distributed over the watershed. Clear sky solar radiation, corrected for topography, is simulated over the elevation grid [45,46], and then corrected for clouds [34]. We correct for canopy attenuation by simulating the transfer of direct and diffuse radiation through various canopy types [47,48].…”