Modelling with CLASS: Representing surface-atmosphere interaction in temperate and boreal forests using the Canadian Land Surface Scheme

The Canadian Land Surface Scheme (CLASS), was employed in off-line tests to represent surface-atmosphere interaction in two temperate forests located near Chalk River, Ontario, and in three boreal forests and a boreal wetland fen, all located near Thompson, Manitoba. CLASS version 2.6 produced a modelled radiation and energy balance that showed broad agreement with measured values at the temperate forests. The surface albedo was modelled to within 1% of observed values, and modelled sensible and latent heat fluxes showed a range similar to observed values. The diurnal range in soil heat flux was exaggerated at all of the test sites. In the mature boreal forest stands, the albedo was overestimated by 3%. The sensible heat flux was underestimated and the latent heat flux overestimated at all of the boreal forest sites, the result of a modelled canopy conductance that was too large.; New canopy conductance algorithms were developed at four of the sites by relating field measurements of stomatal conductance to global solar radiation, vapour pressure deficit, air temperature and soil water suction, using nonlinear regression, and at two of the sites by employing an error analysis of modelled evapotranspiration in relation to the same environmental conditions. Modelled sensible and latent heat fluxes agreed more closely with observed values at all of the test sites when using the new canopy conductance algorithms.; Soil evaporation was poorly modelled, due to difficulty in modelling relative humidity at the soil surface, as required in the so called α method. The α formula was replaced with a β formula, which is based on soil moisture in the top soil layer and soil texture through the field capacity. This improved modelled soil evaporation at two jack pine stands containing sandy soil, where observed values were available, and produced similar behaviour to the a method at two sites where observed values were not available, a black spruce stand and a fen containing organic soils over clay.; CLASS was employed to represent a 1200 km2 region of the Canadian boreal forest, using both the aggregated and the mosaic approaches for representing heterogeneous surfaces. (Abstract shortened by UMI.)...