Coupling a large-scale hydrological model (CWatM v1.1) with a high-resolution groundwater flow model (MODFLOW 6) to assess the impact of irrigation at regional scale

Abstract. In the context of changing climate and increasing water demand, large-scale hydrological models are helpful for understanding projecting future resources across scales. Groundwater is a critical freshwater resource strongly controls river flow throughout year. It also essential ecosystems contributes to evapotranspiration, resulting in feedback. However, groundwater systems worldwide quite diverse, including thick multilayer aquifers thin heterogeneous aquifers. Recently, efforts have been made improve representation models. The evaluation accuracy these model outputs challenging because (1) they applied at much coarser resolutions than hillslope scale, (2) simplify geological structures generally known local (3) do not adequately include management practices (mainly pumping). Here, we apply (CWatM), coupled with MODFLOW, two different climatic, geological, socioeconomic regions: Seewinkel area (Austria) Bhima basin (India). enables simulation impact table on groundwater–soil groundwater–river exchanges, recharge through leaking canals, pumping. This regional-scale analysis assessment model's ability simulate tables fine spatial (1 km CWatM, 100–250 m MODFLOW) when pumping well estimated. Evaluating remains challenging, but results show that reproduction average fluctuations depths without bias can be benchmark objective such We found grid resolution main factor affects depth it smooths incision, while time fluctuations. Finally, use assess groundwater-based irrigation recharge, observations from boreholes.