Supervisors : Lucia Pineau-Guillou and Pascal Lazure (LOPS-Ifremer)
Funding : ANR grant ClimEx
Start date : October 2022
Summary : My PhD is part of the ClimEx project (https://climex.ifremer.fr), which aims to quantify and understand the evolution of extreme sea levels along North Atlantic coasts on decadal to secular time scale. Since the end of the 20th century, the frequency and intensity of the strongest storms are increasing in the North Atlantic (IPCC, 2013). Quantifying and understanding the changes in extreme sea levels is essential to enable the implementation of appropriate coastal adaptation measures. Extreme sea levels are the joint contribution of mean sea level, tide and storm surges. Global mean sea level has been rising over the last century, explaining the main part of the rise in extreme sea levels. However, it is not the unique driver of changes. ClimEx focuses on long-term changes in tide and storms surges, which has raised less attention up to now.
The first objective of this PhD is to characterize how the tide and the storm surges have changed over the last century. Data from tide gauges, satellite altimeters, and seismic stations will be used. Drivers of the changes in tide will be identified, and prediction with a multiple linear regression model will allow to attribute their individual and combined impacts on the variability of tides. The changes in storm surges will be characterized thanks to statistical methods (Generalized extreme value analysis), which allow to compute return levels. The physical drivers of the changes in storm surges will also be identified.
The second objective is to understand the physical causes behind the observed changes. To that end, numerical simulations will be conducted with the TUGO 2D/3D global ocean dynamics numerical model developed by LEGOS (Lyard et al., 2006). TUGO will allow to compute the tide and the surge. It will used in barotropic mode, and will be forced by the Twentieth Century 20CR version 3 dataset (Slivinski et al., 2019), a historic weather reconstruction from 1836 to 2015.
 IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
 Lyard et al. (2006). Modelling the global ocean tides: modern insights from FES2004. Ocean Dyn
 Slivinski et al. (2019). Towards a more reliable historical reanalysis: Improvements for version 3 of the Twentieth Century Reanalysis system. Q. J. Roy. Meteorol. Soc.