Spatially distributed snowmelt rates in a boreal forest basin

Spatial variation in snowmelt rates in the boreal forest can be explained by differences in canopy density. Canopy density, represented as gap fractions (GF), controls both the anlount of shortwave radiation reaching the snov.pack surface and wind speed over the snow surface, which in turn regulates sensible and latent heat fluxes These reductions outweigh any increased contributions from longwave radiation as a result of increased biomass. Differences in the total energy available for melt do not translate to equally proportional changes in melt rates under different canopy densities. As available energy increases, the melt rate increases with decreasing canopy density and the form of therelationship can vary depending on climatic conditions. A good relationship between ground-based GF measurements and a canopy closure index derived from Landsat TM, provides the spatial fabric for the physically-based distribution of snowmelt rates that shows comparable patterns of snow ablation during years of very different climatological conditions. This physically-meaningful method of determining the spatial variability of meltwater delivery to the soil interface provides a better understanding of the heterogeneous active layer development and runoff processes in the boreal forest.