Modelling Climate Change Effects on Groundwater Recharge and Temperature for a Pre‐Alpine Lysimeter

ABSTRACT

Groundwater recharge patterns are expected to shift due to climate change; however, the impact on recharge temperature remains an open question. This study investigates the combined impact of climate change on groundwater recharge rates and temperature in a pre‐alpine region of Switzerland. By applying a 1D numerical model calibrated with unique lysimeter data, daily recharge rates and temperature dynamics were simulated under 47 climate model projections for three greenhouse gas scenarios (RCP2.6, 4.5 and 8.5) from 1981 to 2099. Results project an annual increase in recharge of 7% (RCP2.6) to 20% (RCP8.5), with rates expected to increase from approximately 702 mm a ⁻¹ to a maximum of 770 mm a ⁻¹ (RCP2.6), 785 mm a ⁻¹ (RCP4.5) and 842 mm a ⁻¹ (RCP8.5) by the end of the century, driven primarily by higher winter recharge. Although low recharge rates in summer show minimal change, analysis of the drivers indicates that increased evapotranspiration and decreasing rainfall will extend the periods of low recharge rates into autumn, intensifying potential water stress during warmer months. Moreover, groundwater temperatures are projected to increase together with air temperature, increasing from 10.8°C to 11.6°C (RCP2.6), 12.2°C (RCP4.5) and 13.6°C (RCP8.5) by the end of the century, representing an increase of between 7.5% (RCP2.6) and 26% (RCP8.5). Changes in air temperature mainly drive groundwater warming, whereas changes in recharge rates have minor effects. This study highlights the need for adaptive water management to address shifting seasonal groundwater recharge rates and rising temperatures in pre‐alpine regions.