Missions

In regional numerical models, the unsaturated zone is often represented by Nash cascades (reservoir model) for reasons for computational efficiency, whereas in catchment/local models it is described by the Richards equation. In this context, you will test several representations of aquifer recharge through the unsaturated zone in the EcH2O-iso model by merging and continuing developments already carried out in different versions of the model. You will assess the impact of these two representations on aquifer recharge as a function of the critical zone context (hydroclimatic, geological, land cover), and then look at how this in turn affects root water uptake along the regolith. The following scientific questions will be explored: how does the representation of recharge influence the dynamics of underground flows? How does this representation of recharge processes, coupled with the types of root profiles implemented in the EcH2O-iso model, impact root uptake? These questions could be addressed using numerical experiments on an idealised hillslope through a sensitivity analysis inspecting the simulation of the dynamics of water table levels, water storage in the profile, evapotranspiration components and water transit times in the profile and in outflows. Depending on the time available, this analysis could be transferred to experimental catchments in the OZCAR (Observatoires de la Zone Critique : Applications et Recherche, https://www.ozcar-ri.org/) research infrastructure, where the EcH2O-iso model has already been deployed.

Activities

- Getting to grips with the EcH2O-iso model, its code and online repositories
- Implementation of flow representations in the unsaturated zone in a unified version of the model.
- Comparison of these new representations (recharge flux & storage, evapotranspiration, water transit time) over a gradient of hydroclimatic, geological and plant cover conditions (synthetic cases).
- Writing a scientific publication

Skills

- Solid experience in numerical development and/or modelling (C++, Fortran, Python, and/or R)
- Good level in hydrology or hydrogeology (MS or PhD) with a strong interest in process-oriented modelling
- Interest in an interdisciplinary approach and/or integrating water transit/residence times
- Ability to work and interact as part of a team
- Ability to communicate orally and write in English

Work Context

The OZCAR research infrastructure brings together the critical zone observatories supported by French research institutes. These observatories are places for studying the many processes and interconnections governing the dynamics of this thin layer (from impermeable rock to the lower atmosphere) harbouring the majority of continental life. Among the many research efforts within OZCAR that are developing and using numerical models to describe and predict the pathways and time variation of water transit and storage in the critical zone, some tools have been deployed over several catchments in an attempt to characterise the geological and ecoclimatic controls on critical zone hydrology (Ackerer et al., 2023). A recent effort is based on the EcH2O-iso ecohydrological model (Maneta & Silverman, 2013; Kuppel et al., 2018), which jointly simulates water and energy transfers in a spatialised manner and also allows to track water transit times in the various compartments of the critical zone. Although EcH2O-iso couples different processes (water, energy balance, biomass allocation), the dynamics of hydrological flows in the unsaturated zone and aquifer recharge remain simplified compared with certain real configurations.

This is an extendable fixed-term contract, depending on progress and renewal of credits.

Bibliography : Ackerer, J., et al. (2023). Water Resources Research, 59, e2023WR035672. https://doi.org/10.1029/2023WR035672. Kuppel, S. et al (2018). Geosci. Model Dev., 11, 3045–3069, https://doi.org/10.5194/gmd-11-3045-2018. Maneta, M. P., and N. L. Silverman (2013). Earth Interact., 17, 1–44, https://doi.org/10.1175/2012EI000472.1.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

None