Abstract
Abstract. This paper describes the impact of the various changes made to the Safran–Isba–Modcou (SIM) hydrometeorological system and demonstrates that the new version of the model performs better than the previous one by making comparisons with observations of daily river flows and snow depths. SIM was developed and put into operational service at Météo-France in the early 2000s. The SIM application is dedicated to the monitoring of water resources and can therefore help in drought monitoring or flood risk forecasting on French territory. This complex system combines three models: SAFRAN, which analyses meteorological variables close to the surface, the ISBA land surface model, which aims to calculate surface fluxes at the interface with the atmosphere and ground variables, and finally MODCOU, a hydrogeological model which calculates river flows and changes in groundwater levels. The SIM model has been improved first by reducing the infrared radiation bias of SAFRAN and then by using the more advanced ISBA multi-layer surface diffusion scheme to have a more physical representation of surface and ground processes. In addition, more accurate and recent databases of vegetation, soil texture, and orography were used. Finally, in mountainous areas, a sub-grid orography representation using elevation bands was adopted, as was the possibility of adding a reservoir to represent the effect of aquifers in mountainous areas. The numerical simulations carried out with the SIM model covered the period from 1958 to 2018, thereby providing an extensive historical analysis of the water resources over France.
Highlights
The coupling of hydrogeological models and land surface models (LSMs) aims to represent the water cycle by considering as many physical processes as possible
The SIM system is an offline application whereby the ISBA land surface model is driven by climate data and there is no feedback from the surface to the atmosphere
With the exception of the Carpentras station, where the Land Surface Analysis Satellite Applications Facility (LSAF) infrared radiation (IR) radiation is almost unbiased and the error is the smallest compared to SAFRAN, the scores are better for the high-altitude stations with SAFRAN when the correction is applied
Summary
The coupling of hydrogeological models and land surface models (LSMs) aims to represent the water cycle by considering as many physical processes as possible. In addition to the water balance, LSMs simulate the surface energy balance, which is closely related to the water balance in terms of evaporation In such a coupled system, surface runoff is collected by the surface river system, while deep infiltration of the soil contributes to aquifer recharge. LSMs, whether coupled or not to hydrological models, have been the subject of numerous studies that have improved them over time and have led to a better description and understanding of the key processes governing exchanges at the interface between the surface and the atmosphere and the surface and the subsurface.
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