Résumé
In West Africa Sudanian region, the climate is strongly influenced by seasonal and interannual rainfall variability associatedwith the occurrence of the West African monsoon seasonal cycle. Here, rivers flow intermittently with a dry season that lastsat least six months, and annual river floods of highly variable intensity. Moreover, studies along the soil-plant-river-atmospherecontinuum in this region have highlighted the important role of vegetation water uptake in shaping regional water pathways.Plants may control recharge through water uptake in the root zone, but also through tapping groundwater during and outsidethe rainy season, therefore impacting groundwater-fed river regimes as well. Understanding the complex hydrologicalmechanisms of such systems and their response to climatic and environmental drivers remains a significant knowledge gap,which is critical in the prospect of enhancing the resilience of the populations and ecosystems that rely on these hydrosystems. This scientific question is here addressed in the upper Ouémé basin, covering 10,000 km2 in northern Benin. At this scalewhere hillslope dynamics combine with larger-scale organization of water pathways, we explore the application of a processbased, spatially-distributed model integrating vegetation dynamics as well as the tracking of stable isotopes (2H, 18O) alongflow paths. This combination of features is crucial for gathering information about hydrological system processes using avariety of observational data, ranging from local to basin-level scale. This watershed is a long-term critical zone observatorymonitored by the AMMA-CATCH observatory (www.amma-catch.org) since the late 1990s and features long-termhydroclimatic data records, in addition to measurements of water isotopic composition (18O, 2H) conducted since 2018. Thisnetwork provides critical information to assess model performance, such as records of soil moisture, piezometric level, eddy covariance measurements (including evapotranspiration), and streamflow.This study thus aims to quantify water transfers and stocks, by deploying the EcH2O-iso model with daily simulationsperformed in combination with a 19-year hydroclimatic record (2002 - 2020) and a 3-year isotopic record (2018 - 2020). Modelparameters were manually adjusted until a model-data agreement was reached regarding stream discharge and isotopic recordsat the basin outlet. The first simulations show encouraging results regarding channel dynamics, for both discharge and isotopicsignature. A special emphasis has been placed on the representation of vegetation dynamics through LAI time series, due tothe strong control that vegetation may exert on baseflow generation. Further calibration is ongoing to obtain a betterrepresentation of groundwater depth and relevant output fluxes in this region such as evapotranspiration.