In order to quantify the impact of evapotranspiration phenomena on active layer dynamics in a permafrost-dominated forested watershed in Central Siberia, we performed a numerical cryohydrological study of water and energy transfer using a new open source cryohydrogeology simulator, with two innovative features: the spatially distributed, mechanistic handling of evapotranspiration and the inclusion of the developed numerical tool in the high performance computing tool box for numerical simulation of fluid dynamics OpenFOAM®. In this region, the heterogeneity of solar exposure leads to strong contrasts in vegetation cover, which constitute the main source of variability of hydrological conditions at the landscape scale. The uncalibrated numerical results reasonably reproduce the measured soil temperature profiles and the dynamics of infiltrated waters revealed by previous biogeochemical studies. The impacts of the thermo-hydrological processes on the water fluxes from the soils to the stream are discussed through comparison between numerical results and field data. The impact of evapotranspiration on water fluxes is studied numerically, which highlights a strong sensitivity to the variability of rooting depth and corresponding evapotranspiration at the slopes of different aspects in the catchment.