The energy balance of the winter boreal landscape

Abstract

During the winter of 1993/94 a study to quantify the winter energy balance of the main cover types of the boreal landscape took place. The study was based on the southern edge of boreal forest in Canada. Measurements were made over a mature jack pine stand and a frozen lake. Shortwave albedos of 12% to 14% over the jack pine and 20% to 88% on the frozen lake (both depending on snow cover) were measured. There were correspondingly large contrasts in the total radiation inputs and the turbulent heat fluxes. The mean net all-wave radiation input was large and positive into the forest and negative over the lake. The sensible heat fluxes were of the same sign as the radiative inputs with positive values over the forest peaking at +200 W m-2 and falling to -100 W m-2 over the lake. The evaporation from the forest depended on whether there was snow on the canopy. When the canopy was snow-free, the evaporation was low, about 50% of net radiation but, when there was snow on the canopy the evaporation was large, 4 mm over a 36-h period. The results of these experiments are being used to design much-improved descriptions of boreal forest within the next generation of climate models.