Tide of change: understanding hydrodynamic responses to sea level rise in intertidal environments. Case Study of the Sylt-Rømø Bight, the Wadden Sea

Sea-level rise (SLR) significantly modifies the hydro- and morphodynamics of the tidal flat systems, such as the Wadden Sea (south-eastern North Sea). The current research aims to investigate changes in intertidal dynamics in response to future sea level rise scenarios and their implications for local Wadden Sea habitats, with a focus on the Sylt-Rømø Bight as a case study. With the help of the coastal hydrodynamic model FESOM-C, we simulated a series of SLR scenarios based on the Sixth Assessment Report of the IPCC and morphodynamical projections and analyzed the resulting changes in tidal inundation, local circulation patterns and tidal asymmetry. The simulations were performed on the unstructured mesh with a resolution of up to 2 m in the wetting-drying zone. The results reveal that the intertidal flat areas remain rather resilient to the projected scenarios by 2050. Despite an increasing wetting probability, only 2.2% and 3.4% (13 and 21 km2) of their area are expected to submerge for low and high emissions scenarios (RCP 2.6 and RCP 8.5), respectively. By the end of the century, these percentages increase two and four times, reaching 4.8% and 13.9% (29 and 84 km2) for low and high-emission scenarios. Although an evolution of the peak current velocities is also rather negligible by 2050, a shift in the tidal asymmetry is apparent which points to a gradual transition from a tidal to a lagoon-like system in the future as sea-level rise accelerates. As the projected changes are spatially very diverse, we provide maps of tidal asymmetry in terms of flood/ebb duration, mean and max velocities and discuss the implications for the local habitats.