Modelling the impacts of climate change on groundwater recharge patterns in northern Germany

Schleswig-Holstein, Germany For water management and planning purposes, predictions of how groundwater recharge regimes are expected to change under climate change are of high importance. The northern German state of Schleswig-Holstein has a heavy reliance on groundwater resources, and is expected to experience both increasing precipitation and potential evapotranspiration rates in the future. We implemented the high spatio-temporal deterministic mGROWA hydrological model (100 m, daily) under the full climate ensemble recommended for use in Germany (44 members) until the end of the 21st century to simulate future groundwater recharge changes. For evaluation of climate change impacts, 30-year periods were used. The majority of the climate models show an increase in groundwater recharge rates over the periods 2041–2070 and 2071–2100. This is the case for all three evaluated RCPs (RCP2.6, RCP4.5 and RCP8.5); however, the increases are generally relatively small, with none of the changes classified as significant under the applied robustness test. We also implemented the “climate railguards” concept, which classifies the likely changes as the range between the 15th and 85th percentiles of the climate model results belonging to each RCP. Lastly, a comparison of the application of different spatial areas used for aggregation of results highlights the importance of selecting spatial units appropriate to the water management application. • Groundwater recharge simulated for a climate ensemble until end of 21st century. • Long-term increases in groundwater recharge are predicted for most climate models. • “Climate guardrails” concept used to quantify the likely range of expected changes. • The choice of spatial aggregation scale plays a pivotal role for planning purposes.