Simulating the effects of retreating Urmia Lake and increased evapotranspiration rates on the nearby unconfined aquifer

The unsustainable management of water resources along with climate change impacts have led Urmia Lake to severely shrink since 1995. To quantify the groundwater losses in the surrounding area and to avoid the future worsening of a yet worrying scenario a numerical model is needed. For this purpose, a transient state MODFLOW model (2000-2016) has been calibrated and validated versus hydraulic heads. Good model performances were obtained, allowing to accurately estimate the groundwater budget. MODIS dataset was employed to set up the numerical model to identify temporal and spatial extent of evapotranspiration. Evapotranspiration turned out to play a massive contribution in groundwater outflow showing an increasing trend over time. Several scenarios, considering a different way to implement recharge and evapotranspiration in the modelling routine were assessed. The role of the spatialization of the evapotranspiration extinction depth was investigated by averaging remotely sensed heterogeneous datasets over the model domain. No significant differences in model performance indicators were found. Moreover, a model scenario without human groundwater exploitation and land use change was considered. The results slightly differ from the groundwater budget calculated by the validated model and thus indicating the climate change as the major driver of groundwater depletion in the study area. The implementation of such a model allowed for the assessment of the exchange between the lake and the unconfined aquifer, providing a robust foundation for future sustainable management.