Integrated Water Balance Modeling - Sustainable and Climate-Adapted Water Management

The Borken region in northern Germany faces growing water challenges due to climate change and increasing water demand. Prolonged and intensified summer droughts, coupled with extreme storm events, are becoming more frequent, raising concerns about water scarcity and flood risks. These changes significantly impact stakeholders such as farmers, drinking water suppliers, and private industries, who are increasingly concerned about potential reductions in water use permits. Addressing these challenges requires a holistic water management strategy. Therefore, an integrated water balance model was developed to facilitate regional water resource planning and address ongoing challenges. Plans are underway to enhance this model into an operational system for real-time water resource monitoring and management.

Advanced modeling tools are required for capturing the complex interactions between groundwater, surface water, and the unsaturated zone. The hydrological model for Borken is based on the MIKE SHE software, which enables high-resolution temporal and spatial simulations. The integrated modelling approach offers detailed insights into the water balance of the catchment and integrates all components of the hydrological cycle.

The model incorporates a three-dimensional groundwater flow module based on a hydrogeological model, providing comprehensive insights into the subsurface hydrodynamics. The unsaturated zone, a critical component influencing aquifer recharge and the partitioning of rainfall into infiltration and runoff, is modeled with high precision, accounting for soil properties, moisture content, and evapotranspiration. This detailed representation is essential for predicting the impacts of varying climatic conditions and land-use changes on groundwater recharge rates.

In addition, overland flow processes are integrated into the model, allowing for the simulation of surface runoff during storm events. Further, the model is coupled with a 1D river model based on the MIKE+ software. The coupling ensures a seamless exchange of fluxes between the aquifer and surface water bodies, capturing the dynamic responses of the water system to weather events. The model also includes anthropogenic factors, such as groundwater extractions, irrigation, drainage systems, and hydraulic control structures.

Unlike conventional hydrological models that focus primarily on either groundwater or surface water and apply simplified boundary conditions, the integrated approach used here simulates all hydrological processes in detail. The model is calibrated against both groundwater level measurements and river discharge data, ensuring that processes such as baseflow, interflow, and direct runoff are not merely approximated but are numerically represented and calibrated.

Only through a precise representation of all processes—including the unsaturated zone, groundwater flow, and the interaction between river and groundwater—can both groundwater levels and discharge peaks be accurately modeled. In addition, the integrated model ensures a closed water balance. As a result, the use of an integrated model significantly enhances the predictive quality, offering high confidence in the models ability to forecast water behavior and outcomes.

The model has been calibrated as outlined above and is already being used to assess various retention measure scenarios. By providing this integrated model, stakeholders in the Borken Water Catchment Area are able to make informed decisions, design adaptive water management strategies, and effectively mitigate the risks posed by climate change.