Item: Measurements and modeling of snow energy balance and sublimation from snow
Title: Measurements and modeling of snow energy balance and sublimation from snow
Proceedings: Proceedings of the 1994 International Snow Science Workshop, Snowbird, Utah, USA
Authors: David G. Tarboton, Utah Water Research Laboratory, Utah State University, Logan, Utah 84322-8200, Telephone: 801-797-3172; Fax: 801-797-3663; email: firstname.lastname@example.org
Abstract: Snow melt runoff is an important factor in runoff generation for most Utah rivers and a large contributer to Utah's water supply and periodically flooding. The melting of snow is driven by fluxes of energy into the snow during warm periods. These consist of radiant energy from the sun and atmosphere, sensible and latent heat transfers due to turbulent energy exchanges at the snow surface and a relatively small ground flux from below. The turbulent energy exchanges are also responsible for sublimation from the snow surface, particularly in arid environments, and result in a loss of snow water equivalent available for melt. The cooling of the snowpack resulting from sublimation also delays the formation of melt runoff. This paper describes measurements and mathematical modeling done to quantify the sublimation from snow. Measurements were made at the Utah State University drainage and evapotranspiration research farm. I attempted to measure sublimation directly using weighing lysimeters. Energy balance components were measured, by measuring incoming and reflected radiation, wind, temperature and humidity gradients. An energy balance snowmelt model was tested against these measurements. The model uses a lumped representation of the snowpack with two state variables, namely, water equivalent and energy content relative to a reference state of water in the solid phase at O°c. This energy content is used to determine snowpack average temperature or liquid fraction. The model is driven by inputs of air temperature, precipitation, wind speed, humidity and solar radiation. The model uses physically based calculations of radiative, sensible, latent and advective heat exchanges. An equilibrium parameterization of snow surface temperature accounts for differences between snow surface temperature and average snowpack temperature without having to introduce additional state variables. This is achieved by incorporating the snow surface thermal conductance, which with respect to heat flux is equivalent to stomatal and aerodynamic conductances used to calculate evapotranspiration from vegetation. Melt outflow is a function of the liquid fraction, using Darcy's law. This allows the model to account for continued melt outflow even when the energy balance is negative.
Keywords: sublimation, runoff, snow melting, snow energy
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