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United States Department of Agriculture

Agricultural Research Service

Title: Spatially Distributed Snowmelt Inputs to a Semi-Arid Mountain Watershed

Authors
item Luce, Charls - USDA-FFS
item Tarboton, David - UTAH STATE UNIVERSITY
item Cooley, Keith

Submitted to: Western Snow Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 1, 1997
Publication Date: N/A

Interpretive Summary: Models have been developed to simulate snowmelt from mountainous terrain that account for the variability in melt energy available on different exposures, such as north facing slopes versus south facing slopes. However, methods to account for differences in snowpack accumulation over a watershed have received little attention. This study investigated the effects that different levels of simplification for describing snowpack variability and on simulations of snowmelt rate and timing, and how these different results compared with observed values. Topographic influences and/or drifting and uneven redistribution by strong prevailing winds can be produced significant variability in snowpack depth and density. In such areas, properly accounting for unevenness in the snowpack characteristics can be more important than, accounting for variability in effective incoming radiation in accurately predicting snowmelt and subsequent streamflow. Errors in predicting snowmelt rate and timing can impact streamflow forecasts considerably, thus hampering the proper management of water supply reservoirs. Even rather small errors in expected streamflow volumes and timing can have a significant monetary impact on a multitude of downstream water users.

Technical Abstract: Spatial variability in snow accumulation and melt due to topographic effects on precipitation, drifting,effective solar radiation, and air temperature is important in determining the timing of snowmelt releases. These observations imply that larger scale repre-sentations that ignore drifting could be greatly in error. Detailed measurements of the spatial distribution of snow water equivalence within a small, intensively studied, 26-ha watershed were used to validate a spatially distributed snowmelt model. This model was then compared to basin-averaged snowmelt rates for a fully distributed model, a single point representation of the basin, a two point representation that captures some of the variability in drifting and aspect, and a model with distributed terrain and uniform drift. The model comparisons demonstrate that the lumped, single point representation and distributed terrain with uniform drift both yielded very poor simulations of the basin-averaged surface water input rate. The two-point representation was an improvement bu the late season melt required for the observed streamflow was still not simulated because the deepest drifts were not represented. These results imply that representing the effects of subgrid variability on snow drifting is equally or more important that representing subgrid variability in solar radiation.

Last Modified: 10/20/2014
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