An efficient snow albedo model for the open and sub-canopy

A new model is presented for simulating snow surface albedo in the open and beneath a mixed‐forest canopy. The model has modest input data requirements and is an efficient physically based parameterization that includes the dependency of albedo on solar zenith angle, cloud cover, canopy, snow grain size, litterfall, snowfall, snow depth, and partial snow cover. Measurements used in the model validation include incident spectral irradiances, wavelength‐integrated visible and near‐infrared albedos, snowfall records, snow depth, snow surface litter fractions, and quantity of fine litter in snow cores. Measured and modelled forest snow albedos were less than open snow albedos during the accumulation phase, when there was little or no surface litter. The model predicts lower albedos in the forest during the accumulation phase because of a spectral shift to less reflective wavelengths of incident radiation under the canopy. Snow grain size was important during both the accumulation and ablation phases. Surface litter fraction, incident spectra, snowpack depth, and partial snow cover were important factors lowering forest albedo during ablation. Despite lower mid‐winter albedos in the forest, the snow melted more rapidly in the open. During late ablation, snow albedo in the open became lower than snow albedo in the forest, because of the thinner snow in the open. At the end of the ablation season, partial snow cover affected the albedo in the forest over a longer time period than in the open. Additional work is needed to improve the physical basis of the grain growth model used here and to develop a spatial albedo model for open and forested terrain. Published in 2002 by John Wiley & Sons Ltd.