Changes in tidal dynamics in response to sea level rise in the Sylt-Rømø Bight (Wadden Sea)

Abstract

The Wadden Sea is a complex coastal system where sea level rise (SLR), tidal dynamics, and geomorphology interact non-linearly. Today, the functioning of coastal ecosystems and their services in this region, historically resilient to natural changes in sea level, is at risk due to climate change-induced SLR. This study investigates the changes in tidally induced transport pathways of passive tracers, while providing a comprehensive analysis of tidal inundation, asymmetry, and current velocities under different SLR scenarios projected for 2050. The Sylt-Rømø Bight, a semi-enclosed basin, serves as the study site. Using FESOM-C coastal ocean model with a Lagrangian tracking module on a high-resolution unstructured mesh (up to 2 m resolution in the intertidal zone), we simulate tidal dynamics under SLR scenarios based on projections under low (SSP1-2.6) and high (SSP5-8.5) emission scenarios. Results show submerged areas increase by 2–3%, corresponding to a 4–7% loss of intertidal zones by 2050. As the increased depth and inundation affect the system, tidal channels show contrasting changes in current velocities, suggesting shifts in transport pathways. Meanwhile, weakening tidal asymmetry points to a shift toward a more lagoon-like system, leading to a subsequent reduction in outflowing net transport of passive tracers by up to 10%. This study offers insights into tidal transport patterns in the bight, emphasizing the separation between the southwestern and northeastern regions, both in current and future scenarios. It also provides a methodology for analyzing and explaining SLR-induced changes in the dynamics of shallow, tidally dominated areas. The findings underscore the importance of understanding the complex hydrodynamic response to SLR in coastal areas to meaningfully assess its impacts on tidal ecosystems and to develop efficient mitigation strategies for coastal protection.