Possible evaporation rates from a snow surface with respect to available energy and vapour pressure deficit in the air are discussed. In literature reported measurements and measurements carried out at the University of Luleå are analysed. It is found that for northern areas the total amount of evaporation during the whole snow covered season amounts only to 10–20 mm.
Different formulas for estimating the evaporation from a snow surface are discussed. It is stressed that for forecasting purposes the aerodynamic formula and the profile method should be used only together with energy balance computations. The air density stratification reduces the evaporation rate considerably. A formula for the reduced evaporation rate is suggested. Finally, evaporation is analysed as a transient process, and possibilities of developing more soundly based evaporation models are discussed.
