Development of a soil column model for simulating the water table - vegetation - atmosphere interaction and applications to the catchment scale ; Développement d'un modèle hydrologique de colonne représentant l'interaction nappe - végétation - atmosphère et applications à l'échelle du bassin versant

The representation of the water cycle on land surfaces is essential for climate modeling. Nowadays, the "Land Surface Models" (LSMs) represent soil columns of a few meters deep and they simulate the temporal evolution of the vertical water flows and the interaction with the atmosphere. However, the interaction with a near-surface water table is not taken into account although it strongly influences the evapotranspiration fluxes at the local scale, and therefore the climate at the regional scale. This interaction, which occurs at a smaller scale than the grid scale of the LSMs, is difficult to model. The objective of this PhD is to propose a model that incorporates the impact of a near-surface water table on evapotranspiration fluxes for global climate models. The computation time of the model must be small enough to enable simulations at large spatial and temporal scales. In this context, a new soil column model is proposed with a drainage function that is imposed at the bottom of the column. This function aims at reproducing the temporal evolution of the water table level in interaction with both the infiltration and the evapotranspiration fluxes. The model is tested and validated on numerical experiments and on a real catchment (Strengbach, France). A methodology based on this column model is introduced to estimate the evapotranspiration fluxes taking into account their subgrid variability. This methodology is applied to a catchment whose area is similar to the one of a classic grid cell of LSMs (Little Washita, USA). ; Dans le cadre de la modélisation climatique, la représentation du cycle de l'eau des surfaces continentales est primordiale. Actuellement, les "modèles de surface continentale" représentent l'évolution des flux d'eau verticaux dans des colonnes de sol de quelques mètres de profondeur et leur interaction avec l'atmosphère. En revanche, l'interaction avec les nappes de faible profondeur n'est pas prise en compte alors que leur présence influence fortement les flux d'évapotranspiration à l'échelle ...