General information

Reference

2023-2303  

Position description

Category

F09 Geology - Engineer / Researcher

Job title

Metamodel-based ensemble forecasts of marine flood maps: operational use and uncertainties

Contract

Post-doctoral contrat

Contractual hours

Full-time

Context and contributions of the position

However, marine conditions forecasts and flood early warning systems have gained a significant impulse in the last decades but still mostly follow a deterministic approach or rely on deep simplifications in the processes or scales considered.

Today, there is a growing demand not only to shift towards ever more precise and local marine flooding forecasts, but also to better account for uncertainties, which requires probabilistic methods. Recent advances in high performance computing have enabled numerical weather prediction systems to move from deterministic to probabilistic forecasting using Ensemble Prediction Systems (EPS).

While EPS are increasingly used to predict river flows and induced floods in several countries, it is only emerging for marine flooding. Despite ongoing efforts to develop new generations of high performance oceanographic and phase-resolving models accounting for complex processes, the main challenge still remains the computer power required to run multiple simulations with a chain of models of increasing resolutions (from a hundred meters for coastal waves and surges to a few meters for marine flooding). To overcome this limitation, the “metamodeling” approach made great progresses in this field of application (Lecacheux et al., 2021) and opens up perspectives for intensive and real-time marine flooding computing.

Job description

Joining the French Geological Survey (BRGM) means becoming part of France's leading public institution for Earth Science applications bringing together 1,000 wholeheartedly committed experts across 29 bases in Mainland and Overseas France. BRGM focuses on enhancing geological knowledge and understanding of surface and sub-surface-related phenomena, with a view to: meeting the challenges of environmental changes through innovative projects with societal implications.

In this view, the objective of the post-doc is threefold:

-Produce the ensemble forecasts with the two metamodeling approaches for all cities on the Arcachon Lagoon. This will be based on “replay” ensemble forecasts for recent storm events (like Xynthia and Klaus storms), as well as for synthetic marine flooding events. This task will be conducted in strong interaction with Météo-France (that will provide the ensemble metocean forecasts) to build the simulation plan.

Marine flooding is a phenomenon resulting from the combination between various processes generated at different time and space scales (atmospheric circulation, waves, atmospheric surge, tide) and the local configuration of the coast (coastal bathymetry and elevation, protection structures, etc.). The numerous variables, scales and sources of uncertainty to consider make marine flooding very complex to predict several hours or days in advance.

-Analyse the respective contributions of different uncertainty sources in the two metamodel-based forecast approaches. The considered uncertainty sources are:

• a. The meteorological uncertainty that is related to the weather/marine conditions members that will be provided by Météo-France based on the atmospheric ensemble PEARP (Prévision d'Ensemble ARPege, 35 members, spatial resolution of 8 km);
• b. The metamodel error that is related to the fact that the high fidelity numerical hydrodynamic simulator is replaced by a statistical approximation. Notably, the reconstruction error that is related to the use of dimension reduction techniques to process the spatialized outputs;
• c. The metamodeling procedure to transfer offshore conditions to inland storm-induced responses by investigating the pros and cons of each method.

-Explore the options to use / transfer the information on uncertainties to support the best the decision making for crisis management. This will be conducted in close connection with the workpackages “user needs analysis and feedbacks” and “multiscale vizualisation”, and the partners UMR LASTIG and Keyros.

Profile

Starting date : 01/09/2023
Formation : PhD
Expérience : 1-5 years years of professional experience

The candidate we are looking for has:

PhD thesis in coastal engineering / oceanography with competencies in probability/statistics/data science and skills in programming and data analysis (R or Python).

The post-doc will be performed within the framework of ANR ORACLES (a collaborative project with BRGM, Météo-France, UMR LASTIG and Keyros) which addresses the challenges of producing, translating and visualizing probabilistic forecasts of marine flooding on the Arcachon Lagoon (Gironde, France).

Within the project, two metamodeling procedures to predict flood maps from offshore forcing conditions (water level, waves, wind) are in development: a first one aims to predict predefined categories of submersion type based on flood intensity thresholds, and a second one aims to predict a detailed water level flood map.

While the former is based on methods that have become standard in the literature (like kriging or radial basis functions), the latter requires more advanced techniques combining kriging metamodels (Williams and Rasmussen 2006) and dimension reduction techniques like functional principal component analysis (Ramsay & Silverman 2005) which consists in summarizing the maps by projecting them onto a low dimensional suitable basis set like wavelets or 2D B-Splines (as investigated by Perrin et al., 2021).

If these approaches have shown to be very efficient for many application cases (see introduction of Rohmer et al., 2023; Idier et al., 2021), some questions steel remain about their use in an operational context to produce probabilistic marine flooding forecasts from ensemble metocean forecasts. Firstly, to characterize and compare the uncertainties related to meteorological forecasts and the two metamodeling procedure and secondly, to determine the most suitable approach to produce understandable and practical marine flooding forecasts for crisis managers.

Working conditions

Within an environment that promotes a healthy work/life balance, particularly thanks to remote working, BRGM prides itself on providing a friendly and caring place to work.

Awarded HRS4R certification in 2021, we are committed to supporting you throughout your career at BRGM. We provide you with a range of tools for developing your skills and expertise, with scope for career progression and geographic mobility.

At BRGM, you will gain from such benefits as a 13th month salary, days off compensating for unpaid overtime, meal vouchers, holiday and leisure options.

At BRGM, you are guaranteed a transparent recruitment process. To apply, please send us your application (up-to-date CV and cover letter) by 05/29/2023.

Because diversity matters to us at BRGM, all of our job vacancies are open to everyone!

We will examine your application as soon as the closing date has passed. If your application is short-listed, we will contact you for recruitment interviews during which you will have the opportunity to talk with the recruitment and HR departments as well as a cross-functional department.

Contacts :

Jérémy ROHMER, Déborah IDIER, 3 avenue Claude Guillemin, 45060 Orléans, Cedex 2
Sophie LECACHEUX, Parc technologique Europarc, 24 Av. Léonard de Vinci, 33600 Pessac
Email : j.rohmer@brgm.fr ; s.lecacheux@brgm.fr ; d.idier@brgm.fr

An online interview will be organised if your profile is selected from the first screening.

Position location

Job location

France, New Aquitaine, Gironde (33)

Location