The effect of subgrid scale data variability on the sensitivity of the
surface fluxes is poorly understood for boreal forest landscapes. The objective of this study is to identify the degree to which the small scale vegetation heterogeneity needs to be represented in order to accurately estimate the large scale water and energy fluxes. For this study, a process based water and energy balance model has been improved in the representation of processes specific to climatic and ecologic conditions in high latitudes, such as the impact of an organic layer on the water and energy balance of the forest, parameterization of frozen soil and snow accumulation/ablation, and the effect of open water bodies in the calculation of the radiative energy and water budget. Simulations will be run over the BOREAS Northern and Southern Study Areas using the 30 m Landsat Thematic Mapper (TM) and the 1 km Advanced Very High Resolution Radiometer (AVHRR) vegetation classifications. Validation of model results will be done using observed streamflow and radiosonde budget analyses. The effect of the elimination of small scale heterogeneity in vegetation properties on the water and energy balance fluxes and states will be presented