Development of intertidal flats in the Dutch Wadden Sea in response to a rising sea level: Spatial differentiation and sensitivity to the rate of sea level rise

The Wadden Sea is a unique intertidal wetland area, forming an important hub for migratory water birds. A feared effect of accelerated sea-level rise (SLR) is the gradual loss or even disappearance of the ecologically valuable intertidal flats. To date, the effect of SLR on the time-evolution of the intertidal areas in the Dutch Wadden Sea has not been studied. To explore the sensitivity of the intertidal flats to SLR and the spatial differentiation of the response, simulations are carried out with the reduced-complexity model ASMITA for four sea level rise scenarios: one with a stable rate of 2 mm/yr (current rate), and three with accelerated sea level rise rates to respectively 4, 6 and 8 mm/yr. In addition, a scenario with a linearly increasing rate to 17 mm/yr in 2100 has been added to get an impression of what may happen under more extreme SLR-rates. The results show that the intertidal flats in the larger basins are most vulnerable to drowning. Due to differences in tidal flat geometry, the intertidal flats in the smaller basins mainly reduce in average height, while the intertidal flats in the larger basins mainly reduce in surface area. Within the basins, largest losses are expected to occur just off the land reclamation works and along the western part of each tidal watershed. The intertidal flats are sensitive to the rate of SLR. With doubling the rate of SLR, losses nearly double as well. Complete drowning is not predicted for any of the considered scenarios, but for the larger basins volume losses of nearly 50% by 2100 are predicted for the highest considered scenario. This will transform these basins into more lagoon-like basins, which is expected to have major consequences for the ecology.