Surface-subsurface interaction analysis and the influence of precipitation spatial variability on a lowland mesoscale catchment

The hydrology of the catchments is primarily shaped by the intricate and dynamic interactions between surface water and groundwater. This is particularly evident in lowland catchments, where these interactions assume a complex nature. This study investigated the complex interaction between surface water and groundwater in the transboundary catchment Aa of Weerijs, shared by the Netherlands and Belgium. A hydrological model, MIKE SHE coupled with MIKE 11, was calibrated and validated over twelve years using streamflow, groundwater levels, and evapotranspiration data. The model performance was analyzed using model efficiency parameters i.e., correlation coefficient and Nash-Sutcliffe Efficiency coefficient. The model performed well, with satisfactory simulations of streamflow, groundwater levels, and evapotranspiration dynamics. Groundwater levels rose in winter and declined from April to September due to increased evapotranspiration in summer. Precipitation drove the water balance, with 60 % lost through evapotranspiration. Base flow from subsurface drainage networks significantly contributed to river water. Spatial variability in precipitation minimally impacted streamflow but caused localized fluctuations in groundwater levels. Higher spatial resolution precipitation data led to fluctuations due to local recharge points, yet overall catchment hydrology was unaffected. The findings highlight the importance of surface water-groundwater interactions in lowland catchments. The developed model provides insights for water resource planning and climate change adaptation in the catchment.