Coastal Ocean Modelling for Small Island Developing States in the Eastern Caribbean Sea

Abstract:

Small Island Developing States (SIDS) are at risk of coastal inundation and erosion due to extreme water levels and waves, combined with sea level rise. Waves can contribute to sea level change by generating setup, runup and over-topping, and also cause direct damage to beaches, coral reefs, mangroves, and coastal and offshore structures. Steep volcanic islands such as those in the Lesser Antilles of the Caribbean, may be threatened by long swell waves several times per year, as well as occasional direct hurricane impact on annual to decadal time-scales. The effects of climate change are causing sea level rise and potentially an increased incidence of hurricanes. The slow changes due to increasing sea level (due to global warming) combine with occasional storm-induced surges, waves and regular tides, to modify the return period of extreme water levels and the duration and frequency of events for which waves impact the coast.

We have used regional hydrodynamic and wave models to provide offshore boundary conditions for waves and surges due to hurricanes in the Caribbean Sea. We have compared different forcing fields from reanalysis and synthetic storms to test the worst-case scenarios. Downscaling the wave model to local scale using the SWAN wave model captures nearshore wave processes and wave setup and provides input to the XBeach model to transform the waves across the beach profile. This allows the assessment of wave run-up and cross-shore morphodynamic change. These simulations were performed under wind wave and swell regimes and different antecedent beach conditions, to bring the storm impacts to the relevant local level.

With limited natural, economic and human resources, SIDS have a need for information on climate change impacts, for coastal management, particularly for the economic activities of tourism and fisheries. The SIDS of the eastern Caribbean Sea suffer from limited observational data due to a lack of coastal monitoring, making numerical models even more valuable to fill this gap. We have worked with local stakeholders to understand their data needs and brought together improved access to tide gauge observations and local wave data, as well as global, regional and local water level, wave and storm impact modelling to provide useful tools for coastal planners.