EVAPORATION OF INTERCEPTED SNOW - ANALYSIS OF GOVERNING FACTORS

Insufficient understanding of winter hydrology conditions still hampers progress in predicting springtime discharge. The least known term in the winter water balance is evaporation, particularly of intercepted snow. Recent studies have shown that the evaporation from intercepted snow can be important. This paper elaborates factors governing evaporation of intercepted snow. Measurements with a cut tree-weighing device combined with a method to measure throughfall and drip gave a maximum evaporation rate of 0.3 +/- 0.06 mm/h or 3.3 +/- 0.06 mm/24 hours from a 6-m-high spruce. Calculations of evaporation with a combination equation and different ways to calculate the aerodynamic resistance and the evaporation from a snow-intercepted canopy during melt and sleet events showed that the most important factors for calculating the evaporation were the relative humidity, the aerodynamic resistance, the wind speed, and the intercepted mass. Less important factors were the energy to melt the intercepted snow, the method for calculating reduction in evaporation caused by a partly snow-covered canopy, accuracy in measurement of wind speed, air temperature, and net radiation.