Over the last 3-4 years, the Commonwealth Marine Economies Programme has funded us to work with Caribbean Small Island States. We have carried out a case study in St Vincent from 2017-2020 and in the last 6 months have extended some of the techniques to the wider Caribbean. Two applications of numerical hydrodynamic and wave models will be presented (i) coastal risk from flooding and erosion and (ii) the pollution of beaches by Sargassum and we also discuss the potential for Nature-Based Solutions to coastal defences.
Small Island Developing States (SIDS) are at risk of coastal inundation and erosion due to extreme water levels and waves. Waves can contribute to sea level change by wave setup and runup, and also cause damage to beaches, coral reefs, mangroves, and coastal and offshore structures. SIDS may be threatened by long swell waves several times per year, as well as occasional direct hurricane impact on annual to decadal time-scales. Although direct impacts from individual hurricanes are quite infrequent, especially south of the main hurricane track, these can be most devastating. The effects of climate change are causing sea level rise and possibly an increased incidence of the most severe 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 with which waves impact the coast.
Since 2011 the appearance of large amounts of seaweed on the beaches of the Caribbean Sea has become an almost annual problem e.g. in Barbados and Trinidad and Tobago. On shore, as well as blocking beaches and discouraging swimmers, the Sargassum releases sulphurous odours as it decomposes. Removal is time-consuming, expensive and can damage the beaches. Incoming rafts smother sea grasses and coral reefs, while local fishermen struggle to get into the water, with the huge rafts of seaweed blocking their engines and fishing gear. There is also the risk to the sea turtle population, which comes ashore to nest. Nesting sites can be blocked by the Sargassum or damaged by removal work - and the turtles may become entangled and die. The new source of Sargassum appears to be in the tropical central Atlantic, an area now known as the Great Atlantic Sargassum Belt. Causes have been suggested, such as the increase in discharge of nutrients from the Amazon, due to deforestation and increased use of agricultural fertiliser, as well as changes due to global warming, effecting the ocean circulation and the biochemical composition of the seawater. We examine early results for the transport of Sargassum by a regional NEMO model of the 3D baroclinic, hydrodynamic circulation of the Caribbean Sea.