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Abstract:
In land surface models (LSMs), the land surface components of ESMs, the spatial resolution is usually the one of the atmospheric component or the atmospheric forcing (in offline mode), thus too coarse to represent topographic details and achieve accurate hydrological simulations. Here, we present hydrological simulations over France, using the Organising Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) LSM over France, forced with SAFRAN atmospheric reanalysis at 8-km resolution and hourly time step since 1959 (Vidal et al., 2010), and using a high-resolution river routing network relying on the MERIT-Hydro topography at 2-km resolution (Yamazaki et al., 2019). Each SAFRAN grid is decomposed into a graph of hydrological transfer units (HTUs) based on MERIT-Hydro (Polcher et al., 2022), so that lateral water movements are described at a higher spatial resolution than SAFRAN grids. In particular, it was possible to accurately position over 4000 stations from the national hydrometric network (filtered to drain an upstream area larger than 64 km²), at which the performance of the simulation is assessed over the 1976-2019 period, using classical hydrological indicators on river discharge and evapotranspiration, complemented by trend analysis. Finally, this ORCHIDEE setup will be used to simulate future French river discharges using the DRIAS-2020 climate forcing, consisting in a multi-model multi-scenario ensemble of climate projections selected from the Euro-Cordex ensemble, regionalized and bias-corrected with respect to the SAFRAN reanalysis. We will present an overview of the resulting river discharge projections, which contribute to the national Explore2 project (https://professionnels.ofb.fr/node/1244).
