Global Versus Regional Tidal Modelling: Tides and Sea-Level Rise Revisited

Sea-level has risen by an average rate of 3.2mm yr^-1 between 1993 and 2010, double the rate since 1901. The rate is very likely to accelerate, and the latest IPCC projections suggest up to 1m global mean sea-level rise by 2100. It is well known that large-scale changes in sea-level may affect global tidal dynamics, but tidal models have to date struggled to capture observed long-term trends in the tide gauge record. Here, we use a well-established tidal model to compare the response to realistic and large-scale sea-level changes in both a global set-up with lower horizontal resolution (1/12^o) and in a series of higher-resolution (1/30^o) regional set-ups. Scenarios with and without coastal flooding were included, and simulations using both uniform sea-level rise and changes based on observed sea-level trends were done. The new global runs captures the trends extrapolated from the tide gauge network data in over 2/3 of the stations if sea-level rise is based on observed global trends rather than a uniform increase. The same is true for the higher-resolution regional runs, which also perform better overall than the global model compared to the tide gauge data. The results also show significant changes in tidally driven dissipation rates and potential shifts in tidal mixing fronts, with potential consequences for large-scale biogeochemistry and tidal energy extraction.