The potential effect of climate-change induced consecutive dry or wet years on the freshwater lens of a barrier island (Langeoog, Germany)

Abstract

Study region

Barrier island Langeoog at the German North Sea coast

Study focus

Due to climate change it is predicted that extreme weather events such as droughts and floods will occur more often in future. Since such events strongly influence the groundwater recharge, they will likely affect the freshwater volume on many small barrier islands. This is critical where freshwater lenses are the only source of drinking water. Groundwater abstraction for drinking water supply also influences the freshwater volume. To investigate the potential near-future climate change impacts, the influence of consecutive dry or wet years on the freshwater lens combined with several pumping scenarios is calculated using a density-dependent groundwater flow and transport model. Chosen sub-annual recharge and pumping rates are based on values from the past and, therefore, considered realistic for the island.

New hydrological insights for the region

Five extremely dry years would shrink the volume of the freshwater lens by 20 %. Extremely wet years cause flooding of large areas in the island interior. As the water table adjusts fast to new recharge conditions, flooding within the second winter is almost as severe as in the fifth winter. Tides and storm surges at the mesotidal coast have a great impact on the freshwater lens by constraining the area where fresh groundwater develops and affecting the water table in the interior of the island.