PhD – futurisks

WP1 : Representativeness and uncertainties of the cyclone hazard in the French Overseas Territories (2023-2026)

Aline Zribi

Supervisor(s) : Xavier Bertin, Senior researcher CNRS, La Rochelle Université, LIENSs ; Swen Jullien, Researcher, IFREMER, LOPS ; Guillaume Dodet, Researcher, IFREMER, LOPS

The French Overseas Territories located in tropical zones are particularly exposed to tropical cyclones, which are responsible for violent winds, heavy rainfall, extreme waves and marine submersion. These are complex phenomena (stochastic aspect, highly coupled dynamics, multi-scale interactions, etc.) that remain difficult to characterise, even a posteriori. The aim of this thesis is to reconstruct several major cyclonic events that have occurred since the 1980s, in order to analyse their characteristics and assess the uncertainties associated with the cyclonic hazard in these territories.

WP1/WP4 : Une approche intégrée pour évaluer l’impact des risques climatiques composés dans le contexte des petites îles (2023-2026)

Mirna Badillo

Supervisor(s) : Virginie Duvat, Professor of coastal geography, La Rochelle Université, LIENSs ; Gonéri Le Cozannet, Researcher, BRGM ; Jérémy Rohmer, Researcher, BRGM

Atoll islands will be increasingly affected by climate-related changes, such as sea level rise, rising temperatures, and ocean acidification. These changes will simultaneously affect multiple dimensions of atoll island systems (environmental, social and economic), challenging their resilience. This research aims to better understand the complex interactions between climatic and non-climatic factors that influence the habitability of these islands. It proposes the development of an integrated model, based on Bayesian networks, to assess the future impacts of climate change on key dimensions of habitability (Duvat et al., 2021), such as food security, access to freshwater, the availability of habitable land, and economic activities.

WP2 : Contributions of exceptional distant-source swells to past sea submersions in French Overseas Territories (2022-2025)

Axelle Gaffet

Supervisor(s) : Xavier Bertin, Senior researcher CNRS, La Rochelle Université, LIENSs ; Damien Sous, Professor assistant, Université de Pau et des pays de l’Adour, SIAME ; Gaëtan Dufour, Project manager at Créocéan

Due to the concentration of populations and associated activities in coastal areas, the increase in coastal hazards and the degradation of coral reefs linked to global change, tropical islands will face an alarming increase in coastal risks in the coming decades. Major submersion events can occur in the wake of a tropical cyclone, but also as a result of exceptional distant swells, a phenomenon little known until now. Over the past decade, understanding of the contribution of waves to extreme sea levels has progressed enormously, thanks to studies combining field observations and high-resolution numerical simulations. The representation of tropical sea states must be improved and the the major events of the past decades need to be revisited, to better understand and quantify the importance of setup and infragravity waves in the associated marine submersions.

WP2 : Analysis of Storm Surges and Coastal Flooding Caused by Cyclones in the French Tropical Islands Over the Past Four Decades (2023-2026)

Lola Ormières

Supervisor(s) : Xavier Bertin, Senior researcher CNRS, La Rochelle Université, LIENSs ; Franck Dollique, Professor, Université des Antilles, IRD, BOREA MNHN ; Yann Krien, Assistanr professor, LEGOS

As tropical islands face increasing hazards from extreme sea levels and marine submersion due to climate change, sea level rise, possible intensifying cyclones, and the degradation of coral reefs, this research aims to better understand the key processes driving coastal risks such as marine submersion. The study will combine the analysis of both observational data and numerical simulations. While atmospheric storm surge is relatively well understood, the contribution of wave energy dissipation at the coast to water level along with its interactions with complex features such as rough seabeds (e.g., reefs), currents, and tides remains less studied and poorly understood. Using data from recent field surveys (e.g., Mayotte 2023, Guadeloupe 2017), the project will investigate the physical mechanisms influencing coastal mean water levels during past extreme events, supported by coupled wave–hydrodynamic modeling.

WP2 : Wave transformation processes in coral reef environments (2023-2026)

Mila Geindre

Supervisor(s) : France FLOC’H, Enseignante-Chercheure, Université de Bretagne Occidentale, Geo-Ocean (UMR 6538) ; Damien SOUS, Maître de conférences à l’école d’ingénieurs SeaTech et chercheur à l’Institut Méditerranéen d’Océanologie (MIO) de l’Université de Toulon

This phd thesis aims to improve the spectral parameterization of key processes involved in wave transformation over coral reefs, based on observational data. It specifically focuses on friction, depth-induced breaking, and nonlinear energy transfers. These processes are closely linked to the incident wave hydrodynamics (wave height, period, water depth, etc.) and to the multi-scale geomorphological features of reef systems (reef type, slope, roughness, benthic cover, etc.).

WP3 : L’intérêt d’une approche Passé-Futur pour soutenir l’adaptation côtière au changement climatique : application aux îles françaises du Pacifique (Nouvelle-Calédonie, Polynésie française) (2023-2024)

Maëlys Girault

Supervisor(s) : Virginie Duvat Professor of coastal geography, La Rochelle Université, LIENSs ; Alexandre Magnan, Researcher, Cawthron Institute

The study proposes to demonstrate the importance of long-term history for the analysis of adaptation to climate change through two aspects: the reconstruction of Trajectories of exposure and vulnerability and the investigation of structural and long-term barriers to the governance of adaptation. This deep contextualisation effort should ensure fair and adapted adaptation practices. The analysis focuses on the management of current and future coastal risks of erosion, marine submersion, flooding and the combination of these pressures in two French Pacific territories: New Caledonia and French Polynesia.