Within the French Overseas Territories, Reunion Island is one of the most exposed to cyclone-induced hazards. The Southwest Indian Ocean cyclonic season is officially from 15 November to 30 April. Cyclone tracks often follow a southwestward trajectory. They usually come from the northeast of La Réunion and then continue their course either north or, less frequently, south of the island. Thus, cyclonic waves and storm surge mainly impact the northern and eastern parts of the island. In the past decade, seven cyclones passed within 200km of Réunion Island. In the last thirty years, this number reaches 23.

La Réunion is a volcanic island with two volcanic bodies comprising short torrential rivers. The high rainfall intensity generated a very dense water system with numerous gullies. The Island comprises 13 perennial rivers and several ponds. In the rivers, the water flow can reach considerable values during cyclonic events. For example, a flow of 1 200 m³.s^-1 was monitored in the “Rivière des Galets” during cyclone Dina (2002). Besides, the lack of continental shelf induces great ocean depths very close to the coast. As the coral reefs surrounding the island are very confined, the coast is particularly exposed to high waves and overtopping.

Due to the mountainous nature of the island’s interior, 80% of the population is concentrated near the shore. Thus, several areas with high population densities present an important exposure and vulnerability to both inland and marine floods. The two last strong cyclones were Dumile and Bejisa (resp. in January 2013 and 2014) for which the red level of the ORSEC plan was triggered during 24 hours. The eye of Bejisa passed within 15km from the west coast of Réunion Island (Fig. 3A). The cyclone generated wind gusts around 130-150km/h along the coast and heavy rainfalls, peaking at 800mm at a volcano in Cilaos. Due to the cyclonic swell that broke on the west coast, dozens of people were evacuated in Saint Paul (Fig. 3B) and Saint Leu and the coastal road RN1 was temporarily closed. Numerous houses were inundated and inland and marine flood interaction also resulted in a lot of damages in the port of Saint-Gilles (in the commune of Saint Paul).