Modelling tides and sea-level rise: To flood or not to flood

It has been suggested in recent papers that even moderate sea-level rise (SLR) may have significant and unexpected effects on the tidal dynamics of the European Shelf. The response of the tidal amplitudes varied significantly between the studies, however. Here, it is shown that the way SLR is implemented in the tidal models used for the investigations causes significant differences between the results. When vertical walls are added at the present coastline, the changes are due to (subtly) changed properties of the propagating wave as the water depth is altered, whereas when flooding of existing land is allowed, the response is controlled by the newly introduced dissipation in the new cells. For example, the response of the Irish Sea is controlled by the flooding of estuaries, increasing the tidal amplitudes through the increased dissipation in the newly formed cells as explained by the dampened harmonic oscillator, whereas the North Sea is dominated by the flooding of the Dutch coast which shifts the areas of tidal energy dissipation from the present coastline to the new cells and thus moves the amphidromic points towards the coast. This is further supported by semi-analytical solutions to the Taylor problem. Identifying the processes which control the responses of shelf sea tides to SLR not only increase our knowledge about tidal systems, but also aids predictions of how other shelf sea systems will respond to future climate change.