Modeling staged and simultaneous evacuation during a volcanic crisis of La Soufrière of Guadeloupe (France)

The seismic and fumarollic activity of La Soufrière de Gaudeloupe increased in 1992. Continuing unrest led the Observatoire volocanologique et sismologique of Guadeloupe (OVSG-IPGP) to recommend in July 1999 to the authorities that the volcano alert be set to “Vigilance” (yellow). The OVSG-IPGP has been particularly vigilant and reinforced its monitoring following another significant increase of unrest in 2017 that culminated in magnitude 4.1 felt earthquake and a probable failed phreatic eruption. Volcanic activity remains difficult to forecast precisely, so the only way to stay safe, in case of an impending eruption, is to move away from the threatened area. This can be a major problem for the authorities and the population. In the French overseas departments, despite the presence of several volcanoes, there is limited experience in managing volcanic emergencies, especially in areas with a high population density and strategic assets, such as the Basse-Terre region of Guadeloupe. Therefore, it is crucial to devise and assess an emergency management strategy to identify potential problems and dangers that may arise during a mass evacuation. Crisis exercises can be planned to prepare the authorities and the population, but they are rarely carried out due to the human and resource costs involved. A series of evacuation scenarios are evaluated through simulations. The scenarios model staged and simultaneous evacuations with different speeds of individual response times. The aim of this research is to evaluate the two main evacuation strategies defined in the current volcano emergency response plan for La Soufrière of Guadeloupe, revised in 2018 by the authorities. This paper describes a calibrated agent-based model of mass evacuation and its exploration focusing on the potential staged evacuations of the southern Basse-Terre area. The overall objectives of this research are to: (1) test the evacuation strategy of the current emergency plan, and (2) provide relevant information to stakeholders. The results of these simulations suggest that there is no significant difference between the two evacuation strategies. It is estimated that 95% of the population will be evacuated within 20 h with a simultaneous or a staged evacuation. Whatever the scenario, the simulation results show high levels of road congestion. However, the staged evacuation will significantly reduce the number of vehicles on the network during the peak time of the evacuation and therefore reduce dangerous situations and the potential for adding crises within a volcanic crisis.