Incorporating effects of forest litter in a snow process model

Abstract

Net solar radiation often dominates the snow surface energy exchange during ablation in many conifer forests. Reflection of solar radiation from the snow surface depends not only on snow properties, but also on forest litter lying on and within the snowpack. We know of no validated model reported in the literature that accounts for the influence of forest litter on snow surface energy exchanges. The purpose of this work is to test an existing algorithm's ability to accumulate forest litter in snow layers and to predict the subsequent effect of litter on the snow surface albedo. Field studies in a conifer stand of red spruce-balsam fir in northern Vermont, USA, provided key data for validation, including subcanopy radiation, meteorology, snow depth, and images of litter accumulation. We ran the litter algorithm coupled with the snow model SNTHERM for the ablation season, and predictions compared well with measurements of snow depth, snow surface litter coverage, and snow surface albedo beneath the conifer canopy. Model results suggest that for this forest and ablation season, the current litter algorithm realistically distributes litter in the snowpack through time with validated effects on snow surface litter concentration and albedo, The poor relationship between mean wind speed and change in litter coverage on the snow surface suggest that, for this forest and ablation season, incorporating wind events into the algorithm will not improve the results.