The Latest Improvements in SURFEX v8.0 of the Safran-Isba-Modcou Hydrometeorological Model over France

Abstract. The Safran-Isba-Modcou (SIM) hydrometeorological system was developed and put into operations at Meteo-France in the early 2000's. SIM application is devoted to water resource monitoring, and therefore can help monitoring drought or forecasting flood risks over French territory. This complex system combines three models: SAFRAN analysis of near-surface meteorological variables, ISBA land surface model which aims at computing surface fluxes at the interface with the atmosphere and soil variables, and finally MODCOU a hydrogeological model which calculates river discharges and groundwater level evolutions. SIM model was improved first by reducing the SAFRAN infrared radiation bias, then by using the more advanced multi-layer diffusion surface scheme of ISBA to have a more physical representation of the surface and soil processes. At the same time more accurate and up-to-date input databases for vegetation, soil texture and orography were used and finally in mountainous areas a subgrid representation of the orography using elevation bands was adopted as well as the possibility to add a reservoir to represent the effect of aquifers in mountains. SIM model was run for a 60y period from 1958 to 2018. The present paper describes the changes and demonstrates that the SIM new version performs better than the previous one by comparing a set of selected simulations to measurements of daily streamflow and observations of snow depths.