Evapotranspiration has a major control on continental surfaces dynamics in forested boreal environments. For example, it has strong impacts on active layer thickness, mainly because of its effect on water content within the upper layers of the soil column. These are complex processes, depending not only on climate forcings (atmospheric water demand) but also on physical, geo-pedological and biological properties of the considered areas. Here we propose a numerical investigation of evapotranspiration processes in the active layer of slopes of a forested watershed in Central Siberia. The effect on actual evapotranspiration of the spatial contrasts in terms of exposure, root layer thickness and tree stand density within the watershed are simulated using a recently developed high performance computing cryohydrogeological model, permaFoam.