General information
Offer title : Post-doctoral position in climate simulations & regional rainfall-runoff model (M/F) (H/F)
Reference : UMR7329-VALMER-079
Number of position : 1
Workplace : RENNES
Date of publication : 20 February 2025
Type of Contract : Researcher in FTC
Contract Period : 18 months
Expected date of employment : 1 May 2025
Proportion of work : Full Time
Remuneration : 3451,50€ gross minimum according profesional experience
Desired level of education : Doctorate
Experience required : Indifferent
Section(s) CN : 18 – Earth and telluric planets: structure, history, models
Missions
The person recruited will work at the interface between climate modeling and hydrological modeling in a contexte of a multidisciplinary consortium (ANR NILAFAR).
The remnant lakes of the ancient Abhe mega-lake (with a surface area of 6,000 km2 at the beginning of the Holocene) have been targeted as the object of study in the project.
The aim is to determine the climatic vulnerability of this lake system, considering long-term climatic trends, key climatic events resulting from variability on interannual to multi-century scales, and the influence of changes in vegetation cover and landscapes, whether of natural or anthropogenic origin.
The person recruited will be responsible for two complementary aspects of the project:
• The analysis of regional climate trends, long-term droughts and intense rainfall events at the scale of the Horn of Africa, based on climate simulations over the last 6,000 years. (Expertise P. Braconnot, (laboratory LSCE/CEA – Gif sur Yvette)
• The development and implementation of a more regional-scale rainfall-runoff model of the lake systems of the Afar Depression. The mechanisms and interactions between climate and the watershed of endoreic Lake Abhe (fed by the Awash River in the Afar Depression, Ethiopia, Djibouti) will be explored on the basis of observations available on a historical scale, and then over the last 6,000 years. (Expertise P. Brigode, Geosciences Rennes)
Activities
* The development of innovative analyses of the climate simulations of the last 6,000 years performed in 2023-2024 with the IPSL model in a configuration equivalent in complexity and resolution to that used for climate projections. These analyses should combine statistical and process analyses to understand the different scales of variability simulated over the region, and be able to compare the results with climate reconstructions for East Africa.
* The analyses of extreme situations, with reference to the drought and heavy precipitation events recorded in recent years and the model’s ability to simulate them. A particular focus will be put on the relationship between these events and the teleconnections induced by the El Niño phenomenon in the region.
• Implementation of a hydrological model (rainfall-runoff model) to test hypotheses for identifying the vulnerability and resilience of the hydrological network at the scale of the Afar depression, considering local characteristics and in particular orography whose impact on atmospheric circulation is poorly represented in large-scale climate models. The model will first be calibrated for the recent period from reanalyses and instrumental observations, and the simulations will then be extended to the last 6,000 years. Meteorological data will be provided by transient climate simulations. Test cases will be carried out to study extreme climatic situations and the induced changes in local hydrology over time.
* Consideration of downscaling to link the results of large-scale simulations to hydrological modelling scales in a relevant and, if possible, cost-effective way.
Skills
• PhD in climate sciences, hydrology or statistics applied to geosciences
• Thesis and/or post-doctoral experience desirable in analysis of climate variability and teleconnections, analysis and detection of climate extremes, hydrological modelling, or statistical downscaling methods.
• Experience in handling large datasets (simulations, satellite data, etc.) and using computing clusters
• Taste for running simulations to estimate the sensitivity of a hydrological model to different climatic factors, or to test hypotheses.
• Ability to work at the interface between three laboratories and at the interface between global, regional and local scales
• Autonomy, creativity, reliability, ability to synthesize and work as part of a team
• Computer skills: Unix, Python and R
• English: very good oral and written skills
Work Context
The work lies at the heart of the NILAFAR consortium . It aims to improve understanding of how climate and society affect and are affected by environmental change. Recent advances have enabled us to make progress into these relationships, using analyses of lake sediment cores (Mologni et al., 2024), hydrological modelling of the lake system, as well as transient climate simulations of the past 6,000 years.
This combination of approaches enables us to understand the different scales of climatic variability in the region, their origins and the associated environmental feedbacks. Over the past 6,000 years, long-term drying has been induced by the weakening of the African monsoon due to slow variations in the Earth’s orbital parameters. Thus, the monsoon was more intense in the Middle Holocene than at present, and vegetation was expanding further north than at present.
The changes recorded for the Horn of Africa are part of a large-scale system that has affected the entire Afro-Asian monsoon system. This region is also influenced by interannual variability and, more specifically, the teleconnections generated by the El-Niño phenomenon on the tropical hydrological cycle and precipitation in the region (Mologni et al., 2024). Several studies reported that the impacts of El-Niño have varied over time, suggesting that they are likely to be modified by ongoing warming. In addition, environmental data (e.g. pollen, diatoms, terrigenous flux, lake levels) indicate that the end of the Green Sahara wet period in Africa occurred rapidly or by steps changes, with different timing and dynamics between regions and between East and West Africa (Lézine et al. 2011). It is not yet clear how these changes have modified climatic teleconnections, nor the frequency and/or intensity of rainfall events. As the study of interannual to multidecadal variability in the region is based on climate simulations and reconstructions, the subject will be approached by considering the major drought or flood events of recent years, which have had major consequences for populations, as significant events of interest. Particular emphasis will be placed on joint or cascading events affecting long droughts or heavy precipitating regimes (Braconnot et al. 2019). Hydrological modelling will enable us to better understand regional environmental variations and test how different climatic events such as the end of the wet period, or key events (hyperarid periods around 6.5 and 4.2 kyr cal BP) may have had an impact whose effect affected the environment and populations over a long time. The archaeologists involved in this project, who have been excavating the Afar Depression for many years as part of the PSPCA (Djiboutian Republic, Cauliez & Gutherz 2021) and VAPOR-AFAR (Ethiopia, Khalidi et al., 2020 – Mologni et al., 2022) programs, will be able to contribute during consortium meeting.
The candidate will be assigned to the Géoazur laboratory located on the Sophia-Antipolis technopole. The Géoazur laboratory is a multidisciplinary research unit. It is composed of about 200 researchers and research teachers and structured in 6 thematic teams. The successful candidate will be part of the laboratory’s “RISKS” team, and his employer will be the CNRS. Special feature of this position = the candidate will work under the responsibility of Pierre BRIGODE, in the GEOSCIENCES unit in Rennes (35), lecturer at the University of Rennes. The work will be done in collaboration with Pascale BRACONNOT, of the LSCE, CEA, at Gif sur Yvette and Masa KAGEYAMA (LSCE). Marie REVEL, co-supervisor of the selected candidate and assigned to the GEOAZUR laboratory, will also participate in the hearings.
Constraints and risks
References:
Braconnot, P., Crétat, J., Marti, O., Balkanski, Y., Caubel, A., Cozic, A., Foujols, M.-A., and Sanogo, S.: Impact of Multiscale Variability on Last 6,000 Years Indian and West African Monsoon Rain, Geophysical Research Letters, 46, 14021–14029, https://doi.org/10.1029/2019gl084797, 2019.
Cauliez J., Gutherz X. (Dir), 2021 DJIBOUTI Des paysages & des hommes Regards sur le patrimoine archéologique du lac Abhé., Editions du Cerd, Djibouti, 216p.
Khalidi L., Mologni C., Ménard C., Coudert L., Gabriele M., Davtian G., Cauliez J., Lesur J., Bruxelles L., Chesnaux L., Redae B. E., Hainsworth E., Doubre C., Revel M., Schuster M. & Zazzo A. 9000 years of human lakeside adaptation in the Ethiopian Afar: Fisher-foragers and the first pastoralists in the Lake Abhe basin during the African Humid Period. Quaternary Science Reviews 243:106459, 2020. j.quascirev.2020.106459.
Lezine, A. M., Hely, C., Grenier, C., Braconnot, P., and Krinner, G.: Sahara and Sahel vulnerability to climate changes, lessons from Holocene hydrological data, Quaternary Science Reviews, 30, 3001–3012, https://doi.org/DOI 10.1016/j.quascirev.2011.07.006, 2011.
Mologni C., Revel M., Bastian L., Bayon G., Bosch D., Khalidi L. & Vigier N. Enhanced continental weathering (δ 7 Li, ε Nd) during the rise of East African complex polities: an early large-scale anthropogenic forcing? Comptes Rendus Géoscience 354(G2):319-337, 2022. 10.5802/crgeos.169.
Mologni C., Revel M., Chaumillon E., Malet E., Coulombier T., Sabatier P., Brigode P., Hervé G., Develle A. L., Schenini L., Messous M., Davtian G., Carré A., Bosch D., Volto N., Ménard C., Khalidi L. & Arnaud F. 50-year seasonal variability in East African droughts and floods recorded in central Afar lake sediments (Ethiopia) and their connections with the El Niño-Southern Oscillation. Climate of the Past 20(8):1837-1860, 2024. 10.5194/cp-20-1837-2024.
