85th AMS Annual Meeting

Wednesday, 12 January 2005
Evaluate the snow depletion curve theory in the American River basin with distributed snow model
Eylon Shamir, Hydrologic Research Center, San Diego, CA; and J. Wang, S. Taylor, and K. P. Georgakakos
In numerical hydrologic snow models the Snow Depletion Curve (SDC) is commonly used to explain some of the spatial variability in the snow pack within the modeling elements. This curve relates the Snow Cover Area (SCA) to the ratio between the current Snow Water Equivalent (SWE) and the minimum SWE requires for SCA of 100%. A primary assumption carried in the exploitation of such curves is that the accumulation and ablation processes that control the areal SWE distribution are mainly related to the physical properties (e.g., topography, land cover) and climatic signals (e.g., prevailing wind, mean monthly precipitation distribution) of a given basin. Since these basin properties are assumed stationary over the years with relatively small intra annual variability the derivation of a single representative SDC curve is feasible.

We test the aforementioned assumption in the American River Basin which is located east of Sacramento California and drain the Western slope of the Northern Sierra into Folsom Lake. The NWS snow 17 model which accounts for the current energy and mass states of the pack, was developed in 1-km2 grid cells. The model parameters were spatially distributed to account for radiation variation resulted from land cover and aspect. Two scenarios of model input were compared: The first scenario (hereinafter the static scenario), 6-hour point observed surface temperature was interpolated based on climatic derived lapse rate and the 6-hour cumulative precipitation was interpolated from a point using climatic distribution of monthly precipitation quantity maps from PRISM. In the second scenario (hereinafter Dynamic scenario) the model was forced by dynamically estimated grided (10 km2) precipitation derived from an orographic model and surface air temperature is estimated by the (6 km2) MM5 mesoscale model.

Both scenarios were implemented for the snow season of 2000-04 and compared to the daily MODIS 500 meter snow cover product. The comparison between the scenarios enables the evaluation of the SDC level of sensitivity to continuous and episodic forcing that occurs in the basin. The comparison of the two results pertaining to the two scenarios enables us to identify the appropriate character of the SDC.

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