Multi-hazard Impact Assessment for Volcanic and Storm Hazards: the Saint Vincent Case Study

Abstract

Small Island-Developing States (SDIS) are susceptible to a broad range of risks coupled with a constrained capacity to manage them effectively. The Caribbean is one of three geographical regions in which SDIS are located, with a high vulnerability to multi-hazard events, such as tropical storms and volcanic eruptions. According to the European Commission, the Caribbean is the second most disaster-prone region in the world with extreme climatic events. Based on the EM-DAT database, tropical storms are the most frequent disastrous event in the Caribbean. A tropical storm triggers a combination of coupled hazardous phenomena such as strong winds and heavy rainfall which often leads to floods and landslides. The Caribbean also lies on several active tectonic plates which makes it home to several active volcanoes. There are 21 volcanoes across 11 volcanically active islands. A low-probability high-impact combination of compounding storm and volcanic event happened in 2021 in Saint Vincent where an eruption of the La Soufriere volcano was followed by a storm which triggered several lahars and other cascading effects. Based on historical event records, volcanic eruptions occur on average every 77 to 94 years in Saint Vincent alternating between effusive and explosive eruptions. Meanwhile, tropical depressions affect the island on average once every 3 years for direct hit or brush and 18 years for major hurricane hit. This study will assess the impact of compounding storms and volcanic events in the Caribbean with a case study from Saint Vincent.   A comprehensive multi-hazard risk assessment which considers multiple spatial and temporal scales plays a role in disaster risk reduction and response planning. The present work uses a multi-hazard and multi-phase modular framework based on literature review of historical events in Saint Vincent. Several scenarios are developed that show a variety of hazard types and intensities as well as the impacts. Impact chain models are used to present these scenarios. Impact chains are conceptual models based on cause-effect chains that include all major factors and processes leading to specific risks in a specific context. Compounding scenarios developed resulted in impacts much more severe as compared to the individual events. This study highlights the importance of studying compounding risks and the effectiveness of impact chains assessment for better disaster risk reduction planning and mitigation.   Keywords: multi-hazard, impact assessment, impact chain, volcanic eruption, storm, hurricane, Caribbean.