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Abstract

The majority of observation wells in Brandenburg demonstrate a decrease in groundwater level over the past 50 years at a rate of 1-3 cm/year. The temperatures at the water table, especially beneath urban areas, have risen by up to 1.5°C. Further changes in atmospheric temperature and infiltration rates are expected to put additional strain on the availability of groundwater resources. In this study, we investigate the 70-year-long behavior of the coupled groundwater dynamics and thermal field in the North German basin below Brandenburg. We rely on an existing 3D structural model resolving 12 sedimentary layers with relevant features controlling the shallow groundwater flow, such as permeable Pleistocene glacial valleys, a clay-rich Rupelian aquitard, and a deeply incised erosional boundary between the two. Surface water and climate forcing on the groundwater system are included via time- and space-varying boundary conditions. Recharge and baseflow estimations are derived from a one-way coupling with a grid-based hydrologic model. The simulated hydraulic heads and aquifer temperatures are then validated against time series in observation wells. The model derivatives (e.g., flowlines, aquifer budget, and saturated-zone temperature profiles) are examined to describe the system’s feedback to meteoric water input. The calibrated subsurface conditions will serve as input for a predictive model to forecast the system evolution with respect to IPCC climate scenarios. This study highlights the importance of thermo-hydraulic modeling together with the integration of subsurface and surface data for reconstructing aquifer dynamics and, ultimately, for groundwater resource management.