| Abstrakt: |
Fresh coastal groundwater is a valuable water resource of global significance, but its quality is threatened by saltwater intrusion. Excessive groundwater abstraction, sea‐level rise (SLR), land subsidence and other climate‐related factors are expected to accelerate this process in the future. The objective of this study is to (a) quantify the impact of projected climate change and (b) explore the role of individual hydrogeological boundaries on groundwater salinization of low‐lying coastal groundwater systems until 2100 CE. We employ numerical density‐dependent groundwater flow and salt transport modeling for this purpose, using Northwestern Germany as a case. Separate model variants are constructed and forced with climate data, that is, projected SLR and groundwater recharge, as well as likely ranges of other hydrogeological boundaries, including land subsidence, abstraction rates and drain levels. We find that autonomous salinization in the marsh areas, resulting from non‐equilibrium of the present‐day groundwater salinity distribution with current boundary conditions, is responsible for >50% of the salinization increase until 2100 CE. Sea‐level rise, land subsidence and drain levels are the other major factors controlling salinization. We further show that salinization of the water resources is a potential threat to coastal water users, including water suppliers and the agrarian sector, as well as coastal ecosystems. Regional‐scale uplifting of drain levels is identified as an efficient measure to mitigate salinization of deep and shallow groundwater in the future. The presented modeling approach highlights the consequences of climate change and anthropogenic impacts for coastal salinization, supporting the timely development of mitigation strategies. Plain Language Summary: Our study focuses on fresh groundwater near coastlines, which is crucial for drinking water, agriculture, and natural ecosystems, but is at risk of becoming salty due to mixing with saline groundwater. We investigate how climate change, including sea‐level rise, changing groundwater recharge and subsiding land surfaces, might make this problem worse by 2100 CE. Northwestern Germany, located at the North Sea, is used as a case, and numerical groundwater models are employed to simulate the groundwater development in the study area. We find that the current groundwater salinity distribution is not at equilibrium with present‐day boundary conditions, which is a primary reason for an expected salinity increase by 2100 CE. Rising sea‐levels and the design of the marsh drainage system are other key factors. We show that raising mainland drainage levels would be an effective way to reduce future salinization in both deep and shallow groundwater. The methods applied in this study could help other coastal areas to understand the implications of future groundwater salinization. Key Points: We show that autonomous salinization is a key process driving salinization of low‐lying coastal groundwater systemsWe find that sea‐level rise and land subsidence are other major factors amplifying future groundwater salinizationWe describe how salinization of coastal fresh groundwater impacts different water users [ABSTRACT FROM AUTHOR] |
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