The Wadden Sea of the German Bight stretching from Den Helder in The Netherlands to Skallingen in Denmark is a prototype for a coastal region under threat by sea level rise. Over 50% of the Wadden Sea area consists of intertidal flats which are submerged by water only during a part of the tidal cycle. This shapes the unique coastal ecosystem of the Wadden Sea which could survive the sea level rise of the last centuries by accumulating sediment from the North Sea at a rate which made the inter-tidal flat level keeping pace with sea level rise.

The key question is, up to which rate of increased sea level rise the sediment accumulation in the Wadden Sea will be sufficient. This is a complex question since the sediment fluxes into the Wadden Sea depend on the rate of sea level rise itself, on other consequences of climate change as well as on sediment availability in a highly non-linear way.

It is known that net sediment fluxes are driven by tidal asymmetries caused by non-linear overtides and horizontal density differences due to net-precipitation and run-off as well as cooling or heating of the Wadden Sea. The characteristics of non-linear overtides depend on sea level rise (more energetic tides, increased tidal range) and the horizontal density gradients may substantially alter with climate-related changes in precipitation/evaporation and cooling/heating. Furthermore, sediment fluxes are sensitive to wind intensity and direction, which are also susceptible to climate change. Although the knowledge about sediment dynamics in the coastal zone allows for realistic model simulations of sediment transport in the Wadden Sea, projections of morphodynamic change are still using highly simplified vertically integrated models. The knowledge gained from such models is therefore strongly limited.

The leading objective of this project is therefore to assess possible morphological responses of the Wadden Sea to increased sea level rise and other aspects of climate change under conditions of changed sediment availability, using a process-based model. With this, the major driving forces for sediment transport in the Wadden Sea will be included. First, these simulations will be carried out in a systematic way using idealised bathymetries, identifying the most critical processes of morphodynamic change in the Wadden Sea. Using these bathymetries, impacts of sea level rise on the sediment accumulation can be assessed in combination with other changes of external forcing (precipitation-evaporation, cooling-heating, wind-wave forcing). In a second phase of the SPP, anticipating further increasing supercomputing capacities, these simulations will be carried out for realistic tidal basins in the Wadden Sea. In both phases, the dynamics of salt marshes will be explicitly included.