Sensitivity to global changes in the humid West-African critical zone using an integrated high-resolution modeling approach.

Laboratoire de rattachement  : LTHE
Encadrant : Jean-Martial Cohard (jean-martial.cohard
Téléphone : 04 76 51 45 64
Co-encadrants : Basile Hector (basile.hector

West Africa is particularly vulnerable to global changes. While precipitation intensification is already observed, the population is also expected to double in the early 2040, implying rapid changes in land use. These will induce significant changes in the continental water cycle within the Critical Zone (CZ), defined as the part of the continental surface from the basement to the canopy top. For instance, river flows and evapotranspiration feedbacks on the monsoon system will be affected. Integrated approaches are needed for understanding CZ behaviors and predicting its evolution. The goal of the internship is to characterize the behavior of the Ouémé River (Benin) which undergoes significant and repeated flood events when submitted to the effect of precipitation intensification scenarios and simple land-use change scenarios.

Recent developments in physically-based CZ models allow to study interactions within the CZ (for instance between groundwater and evapotranspiration processes) at large scales (up to the continental scale) by keeping a high resolution (< 1km²) thanks to the use of supercomputers and parallel implementations. This is the case for instance of the coupled ParFlow-CLM model developed at the Colorado School of Mines. The student will set up PF-CLM at a stake scale in the flood-prone humid Ouémé catchment in Benin to analyze the system sensitivity to changes. The work will benefit from the team experience in using this model at a small catchment scale in the upper-Ouémé section and the international PF-CLM network on large scale development (continental US, Europe). It will also benefit from the large database of the AMMA-CATCH observatory. The first major challenge will concern the large-scale hydrodynamic parameterization based on small-scale knowledge in the hard-rock basement zone and large-scale observations (geologic maps, remote sensing-derived datasets). Second challenge will regard the resolution change : how to represent 10m length-scale observed processes in a 1000m model cell. This study is a first step toward the next scale, namely West-Africa, which includes other environmental conditions.