Effect of vegetation on the energy balance and melting of snow in the Rocky Mountains (Invited)

V. Mahat
David G. Tarboton, Utah State University

Abstract C41B-0629 presented at 2013 Fall Meeting, AGU


Forest canopy interception of snowfall results in smaller snow accumulation in forest area than in open area. The forest canopy also modifies the energy exchange between the snow surface and the atmosphere, and alters the sublimation and melting of sub-canopy snow relative to open area. To better quantify snow-vegetation-atmosphere interactions we developed theory and model parameterizations for what are essentially three new contributions to modeling snow accumulation and melt in heterogeneous mountain watersheds. These are a component for the representation of the transmission/attenuation of radiation through a forest canopy including absorption and scattering, a component for snow interception and unloading, including melt and sublimation of intercepted snow, and a component for the turbulent energy exchanges between the snow surface, canopy and atmosphere above that incorporates aspects of the two source model developed for evapotranspiration. These three components represent new functionality which we added to the Utah Energy Balance snowmelt model to provide improved capability to predict the surface water input and runoff from snowmelt in heterogeneous watersheds. The model was evaluated by comparing model simulated values with observations made in different vegetation classes at forest study areas in the Rocky Mountains of Utah and Colorado, USA. The model was able to capture the sensitivity of beneath canopy net radiation and turbulent fluxes, and snowmelt to vegetation class consistent with observations and achieve satisfactory predictions of snow accumulation and melt from forested areas from parsimonious practically available information. The model is simple enough to be applied in a spatially distributed way, but to still relatively rigorously and explicitly represent variability in canopy properties in the simulation of snowmelt over a watershed.