Limits and perspectives to assessing morphological resilience in the Wadden Sea

Abstract

The world heritage site Wadden Sea on the Northwestern European continental shelf is the world’s largest coherent channel-shoal environment. It hosts numerous unique ecosystems and serves as natural coastal protection for the mainland. As one of the world’s most frequently monitored coasts, its morphological evolution under relative sea level rise (SLR, includes vertical land movement) was studied intensely and can be considered as benchmark for the adaptation of other tidal flat and marsh areas.

Recent studies focused on the accretion of intertidal flats under SLR because their submergence poses severe negative consequences for coastal protection and biodiversity. These morphometric analyses reported a general steepening tendency, characterized by deepening tidal channels in combination with accreting tidal flats. Miao et al. (M25 in the following) suggest that these previously reported accretion rates were overestimated due to an inconsistent number of small-scale features in long-term topographic datasets, e.g., creeks and gullies, resolved only in more recent topography. While bias arising from combining modern high-resolution topography with interpolated conventional datasets is a valid concern, the evidence provided in M25 and limitations of the underlying topography dataset cannot support far-reaching conclusions such as diminishing resilience. In this work, we discuss the conceptual challenges of defining coastal morphological resilience und critically examine M25’s methods. Our supplement describes the uncertainty of topography datasets (S1), pitfalls in morphometric analysis (S2), presents implications of the harmonization proposed by M25 on an integrated morphometric analysis (S3), and proposes ways forward (S4).