Validation of the Canadian Land Surface Scheme (CLASS) for a subarctic open woodland

This study reports on testing of the peatland version of the Canadian Land Surface Scheme (CLASS) for simulating the energy balance of subarctic open woodland terrain. Model results are compared against several years of measu red data from a site near Churchill, Manitoba. In contrast to most forest e nvironments, the floor of the open forest plays a large role in total ecosy stem energy exchange. This behaviour presents a significant challenge for l and surface models like CLASS and their simplified treatment of vegetation canopies. Simulations of summer energy balance for seven years encompassing a wide range of meteorological conditions produced consistent results. Roo t mean square errors for sensible and Intent heat fluxes fell between 11 an d 28 W m(-2). CLASS consistently underestimated slightly the daily latent h eat flux and overestimated the sensible heat flux, average mean bias errors being -7.6 and 9.1 W m(-2), respectively. The soil heat flux was less well represented. In general, CLASS was able to capture the diurnal and seasona l behaviour of the measured fluxes under a range of conditions with reasona ble accuracy. In a full year simulation, CLASS reproduced the annual variat ions in energy balance with some discrepancies associated with some accumul ation and ablation periods. The model performance was sensitive to both sno w density and specification of the surface cover Recommendations for improv ing the model for subarctic woodlands and terrain types with similar featur es are discussed.