Ecohydrological modeling in three contrasted watersheds from OZCAR research infrastructure

The French OZCAR Critical Zone Observatory network offers the opportunity to performmulti-site studies to explore the critical zone functioning under contrasted climate, geology, vegetation and land use. In this study, we investigate how soil-water-vegetation interactions control the hydrologic response of three watersheds, and we present recent results obtained by taking advantage of a large database for critical zone sciences at the French national scale and using the novel fully spatially distributed and physically based ecohydrological model EcH2O-iso (Kuppel et al., 2018). The ecohydrological functioning of three contrasted watersheds was investigated in detail with (1) the Kervidy-Naizin watershed characterized by an oceanic climate (north-west of France), a metamorphic bedrock and an intensive pig and dairy farming; (2) the Aurade watershed, a watershed with a semi-continental oceanic climate (south-west of France), a sedimentary geological substratum and an extensive crop cover with a wheat-sunflower rotation and; (3) the Strengbach watershed characterized by a mountain climate (north-east of France), a granitic bedrock, and a beech-spruce forest cover without agriculture. Results fromecohydrological simulations underline the importance of soil and regolith thicknesses as well as spatial variability of hydrodynamic parameters in the shallow subsurface for controlling stream discharge at watershed outlets. The seasonality of the vegetation cover and evapotranspiration is also a key feature to understand variations of total water storage and water transit time in watersheds. Intercomparison between the three watersheds also shed light on differences in water storage dynamics and allows us to better identify the key soil-water-vegetation interactions controlling storage dynamics. Modeling robustness was evaluated by a large number of variables including stream flow, water level in piezometers, and evapotranspiration fluxes measured from climatological stations and flux-towers located in the watersheds. This study highlights the interest of crossing different critical zone observatories for an integrated understanding of soil-water-vegetation interactions and their control on water storages and water transit times.