Hydrological variability of major French rivers over recent decades, assessed from gauging station and GRACE observations ; Evaluation de la variabilité hydrologique des grands fleuves français au cours des dernières décennies à partir des stations de jaugeage et des observations GRACE

International audience ; This study was carried out in the framework of the Surface Water and Ocean Topography (SWOT) programme of the French National Centre of Space Studies (CNES). Based on discharge measurements and Gravity Recovery and Climate Experiment (GRACE) determination of total water storage (TWS), we have investigated the hydrological variability of the main French drainage basins (Seine, Loire, Garonne and Rhône) using a wavelet approach (continuous wavelet analyses and wavelet coherence analyses). The results of this analysis have shown a coherence ranging between 82% and 90% for TWS and discharge, thus demonstrating the potential use of TWS for characterization of the hydrological variability of French rivers. Strong coherence between the four basin discharges (between 73% and 92%) and between their associated TWS data (from 82% to 98%) suggested a common external influence on hydrological variability. To determine this influence, we investigated the relationship between hydrological variability and the North Atlantic Oscillation (NAO), considered as an index of prevailing climate in Europe. Basin discharges show strong coherence with NAO, ranging between 64% and 72% over the period 1959–2010. The coherence between NAO and TWS was 62% to 67% for 2003–2009. This is similar to the coherence between NAO and basin discharges detected for the same period. According to these results, strong influence of the NAO was clearly observed on the TWS and discharges of the major French river basins. ; Cette étude a été effectuée dans le cadre du programme Surface Water and Ocean Topography (SWOT) du Centre National d’Études Spatiales (CNES). La variabilité hydrologique des principaux bassins versants français (Seine, Loire, Garonne et Rhône) a été étudiée à l’aide de l’analyse en ondelettes. Ces méthodes ont été appliquées aux données de débits et à la variation des stocks d’eau issue de la mission spatiale GRACE (Gravity Recovery and Climate Experiment). Une forte cohérence, comprise entre 82% et 90%, a été ...