Addressing the challenges of climate scenario-based impact studies in modelling groundwater recharge on small barrier islands at the German North Sea coast

Abstract

Study RegionBarrier island at the German North Sea coast Study FocusDrinking water supply on small barrier islands strongly depends on extractions from their freshwater lens below the island when no pipeline to the mainland exists. The shape and extend of the lens is influenced by sea level change, abstraction and groundwater recharge, while groundwater recharge is the only inflow of freshwater into the system. To ensure sustainable use of groundwater in the future within changing climate conditions, knowledge in long-term groundwater recharge is required which can be obtained by climate scenario-based simulations. However, hydrological modelling on small barrier islands faces challenges, such as the lack of calibration and validation data. In addition, the historical long-term mean of main climate variables, such as precipitation and temperature, is represented inadequately in available regional climate models. In order to quantify previously mentioned topics, a water balance model was set up for the small barrier island Norderney. Subsequently, climate change impact on groundwater recharge was simulated.New hydrological insights for the region: The applied methodology increases plausibility and confidence in impact assessments compared to a-priori model applications. Future long-term development of groundwater recharge is highly dependent on the underlying climate model and emission scenario, but also affected by large uncertainties throughout the model chain, e.g. by the approach used for bias-correction. The scenario results can be directly used as forcing data for three-dimensional groundwater models.