Multi-Hazard Risk Assessment due to Hurricane Activity: Case Study of St. Martin, the Caribbean

Student Report

Every year hundreds of thousands of people are affected by natural disasters that occur due to various physical phenomenon. They include earthquakes, tsunamis, volcanic eruptions, and hurricanes. In this research the focus is on hurricane events and the impact they have on a community. The ability for a community to bounce back is defined by their disaster resilience which, in turn, depends on their ability to identify vulnerabilities and prepare for the inevitable. Within this line of research, one of the main challenges is defining local risk due to hurricane events, especially when considering more than one hurricane-induced hazard. Furthermore, the challenge becomes even greater when analysing risk in locations around the world where data availability is scarce. This study aims to clarify and improve the existing methodology to define multi-hazard risk due to hurricanes. This methodology is verified by applying it to the case study of St. Martin, in order to delineate hurricane risk on the island. St. Martin was chosen to investigate, as it is a Small Island Developing State in the Caribbean that recently suffered immeasurable damages during Hurricane Irma (September 2017), and is still struggling to recover. The two hazards that were considered, in the application of the methodology, were hurricane-induced winds and hurricane-induced coastal flooding. In the case of St. Martin, hurricane-induced winds were found to contribute to 98% of damages due to Hurricane Irma, when compared to the coastal flood damages. Coastal flooding was found to be due to both increased storm surge levels and wave-induced flooding, showing that neither one is negligible for a reef island like St. Martin. Storm surge variation around the island was found to be minimal due to the scale of the island, and the fact that storm surge was predominantly pressure driven. Validation of the models to simulate hazards and impact on St. Martin proved to be challenging. An unconventional data source was used to validate the flooding model, which included analysis of Twitter data of images posted during Hurricane Irma. This is an example of a solution of how to deal with data scarcity in hazard modelling. The risk assessment of St. Martin involved simulating synthetic hurricane track scenarios and determining their respective wind and flood damages on the island. Combining the respective damages was done by including a damage threshold to ensure combined damages did not exceed 100%. The applied framework resulted in a hurricane risk map of St. Martin indicating Expected Annual Damages per community. The intention of the improved methodology is to apply it to a hurricane risk prone region, like St. Martin, and to use the outcome to delineate hurricane risk. This indicates hot-spots in the region of interest and improvements to disaster resilience can be discussed. The approach of Build Back Better is highlighted in this research to show how this risk map can be interpreted and what the results mean. Three branches are discussed, namely building back stronger, which involves ensuring infrastructure can resist more extreme events in the future.