The effect of in situ evaporation on perceived snow distribution in partially clear-cut forests

Differences in snow found under trees and within clearings of partially clear-cut forests are variously attributed to interception, redistribution and/or aerodynamic trapping of the falling snow. Measurements in Alberta during 1973 revealed that the snow present on the tree- or clearing-side of the sunlit edges of 60 to 120 m diameter circular clearings was less than at the shaded edge, raising a fourth possibility; that of differential evaporation or melting of snow between the sunlit and shaded portions of clearings. The evaporation from snow during precipitation-free days in January through March 1985 was 0.18 mm d-1 under the trees on the shaded edge; 0.42 mm d-1 under trees on the sunlit edge. The 4 to 7 mm of evaporation estimated during the 22 snow-free days in February 1973, was less than 1/3 the 25 mm of precipitation that occurred. On March 1, the snow measured on treed and open sides of the north edge was less than the amount measured there on February 1. More than 18 mm of snow loss were unaccounted for by in situ evaporation from the snowpack.