Evaluation of seagrass as a nature-based solution for coastal protection in the German Wadden Sea under end of the century sea level rise projections

Climate change, along with sea-level rise and shifting hydrodynamics, threatens coastal systems such as the Wadden Sea. At the same time, nature-based solutions (NbS) have gained prominence in coastal protection, recognizing the buffering role of vegetation such as seagrass. This study evaluates hypothetical seagrass meadow extension scenarios as NbS, assessing their potential to mitigate coastal hazards under present and future climate conditions. Time-slice simulations for the years 1997 and 2090 were conducted using the unstructured-grid SCHISM modeling framework, which couples hydrodynamics, wave action, sediment dynamics, and a vegetation module representing first-order seagrass effects on flow and turbulence. Pairwise simulations under the RCP8.5 scenario with and without vegetation were conducted  to quantify attenuation of currents, wave energy, bottom stress, and sediment concentrations. Results show that despite a ~20% decline in relative attenuation efficiency under sea-level rise, seagrass meadows retain substantial damping capacity. Wave heights were reduced by 30% in shallow areas, with even greater absolute reductions in deeper zones of enhanced wave activity. Bottom stress attenuation frequently exceeded 60%, accompanied by lower near-bed sediment concentrations.

Although limited to hydrodynamic effects and time-slice simulations without morphodynamics, this study highlights the continued importance of seagrass in coastal protection and the need to integrate ecological components into climate adaptation strategies.