The snow melt calculations are controlled by “Forest canopy”, i.e. the proportion of ground surface covered by forest. Depending on the proportion of forest in a catchment area, various factors will play a greater or smaller role as regards snow melt under different weather conditions. The various factors might be rain on snow, strong winds, strong solar irradiation, etc. In Basin properties under “Forecast canopy (fraction)” you enter the proportion (between 0 and 1) of the area that is covered by forest.