Abstract
This study explores the projected responses of tidal dynamics in the North Sea induced by the interplay between plausible projections of sea-level rise (SLR) and morphological changes in the Wadden Sea. This is done in order to gain insight into the casual relationships between physical drivers and hydro-morphodynamic processes. To achieve this goal, a hydronumerical model of the northwest European shelf seas (NWES) was set-up and validated. By implementing a plausible set of projections for global SLR (SLRRCP8.5 of 0.8 m and SLRhigh−end of 2.0 m) by the end of this century and beyond, the model was run to assess the responses of the regional tidal dynamics. In addition, for each considered SLR, various projections for cumulative rates of vertical accretion were applied to the intertidal flats in the Wadden Sea (ranging from 0 to 100% of projected SLR). Independent of the rate of vertical accretion, the spatial pattern of M2 amplitude changes remains relatively stable throughout most of the model domain for a SLR of 0.8 m. However, the model shows a substantial sensitivity toward the different rates of vertical accretion along the coasts of the Wadden Sea, but also in remote regions like the Skagerrak. If no vertical accretion is assumed in the intertidal flats of the Wadden Sea, the German Bight and the Danish west coast are subject to decreases in M2 amplitudes. In contrast, those regions experience increases in M2 amplitudes if the local intertidal flats are able to keep up with the projected SLR of 0.8 m. Between the different scenarios, the North Frisian Wadden Sea shows the largest differences in M2 amplitudes, locally varying by up to 14 cm. For a SLR of 2.0 m, the M2 amplitude changes are even more amplified. Again, the differences between the various rates of vertical accretion are largest in the North Frisian Wadden Sea (> 20 cm). The local distortion of the tidal wave is also significantly different between the scenarios. In the case of no vertical accretion, tidal asymmetry in the German estuaries increases, leading to a potentially enhanced sediment import. The presented results have strong implications for local coastal protection strategies and navigation in adjacent estuaries.
Highlights
Climate change induced sea-level rise (SLR) is one of the major challenges for low lying coastal communities and coastal infrastructure, in the future and already today (Nicholls and Cazenave, 2010; Arns et al, 2017)
To analyze the responses of the North Sea tides to SLR and morphological changes in the Wadden Sea, the assessment considers the likely alterations in the amplitudes of the dominant semi-diurnal tidal constituent M2
Hendershott and Speranza (1971) introduced a dissipative boundary condition to Taylor’s solution, while Rienecker and Teubner (1980) added the effect of bottom friction. Both incorporated effects lead to a shift of amphidromic points in cross-basin direction, even though the displacements of amphidromic points are different. Based on these idealized solutions, M2 amplitude changes can generally be explained by different spatial patterns of energy dissipation, which lead to varying migrations of amphidromic points in return
Summary
Climate change induced SLR is one of the major challenges for low lying coastal communities and coastal infrastructure, in the future and already today (Nicholls and Cazenave, 2010; Arns et al, 2017). Throughout the twentieth century (1901–1990), a mean global SLR of 1.4 mm/yr was observed (Oppenheimer et al, 2019). Projections from the Intergovernmental Panel for Climate Change (IPCC) indicate that the global mean sea-level (MSL) will rise by 43 cm (lowemission scenario RCP2.6) to 84 cm (high-emission scenario RCP8.5) by the year 2100, in relation to the observed MSL in the time span of 1986–2005 (Oppenheimer et al, 2019). Following the RCP8.5 scenario, sea-levels will continue to rise unabated beyond the twenty-first century, with a likely range of 2.3–5.4 m by the year 2300 if no effective mitigation measures are implemented to reduce greenhouse gas emissions (Oppenheimer et al, 2019). For the North Sea region, which is in the focus of this study, recent rates of SLR of 4.00 ± 1.53 mm/yr (1993–2009) even surpass mean global SLR (Wahl et al, 2013)
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