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Variations du cycle hydrologique continental en France des années 1850 à aujourd'hui

Abstract : The main objectives of this work are to characterize the evolution of the continental hydrological cycle over France from 1850 to present, and to understand the hydrological and climate mechanisms involved. Long-term river flows observations of river flows are scarce and the other variables of the continental hydrological cycle (soil moisture, snow cover and evapotranspiration) are virtually not observed on such longtime scales. To overcome this observational gap, numerical modelling is used. First, hydrometeorological reconstructions available over France through the twentieth century are analyzed. These reconstructions are based on a new approach. It combines the results of long-term atmospheric reanalyses downscaled with a stochastic statistical method and homogenized monthly precipitation and temperature observations to derive the meteorological forcing needed for the physically based hydrological model. The evaluation of these reconstructions show that using homogenized observations to constrain the results of statistical downscaling help to improve the reproduction of precipitation, temperature, and river flows variability. In particular, some unrealistic long-term trends associated with the atmospheric reanalyses are corrected. The analysis of the reconstructions confirms that the multidecadal variations previously noted in French river flows are mainly a climatic-driven. Moreover, the analysis shows that the other variables of the french continental hydrological cycle, like evapotranspiration, soil moisture or snow cover, are also characterized by multi-decadal variations. Depending on the region, the persistence from spring to summer of soil moisture or snow anomalies generated during spring by temperature and precipitation variations may explain river flows variations in summer, when no concomitant climate variations exist. Based on the recent release of the NOAA 20CRv2c long-term atmospheric reanalysis, available from the 1850s, a new hydrometeorological reconstruction is developed over the Seine catchment. [...]
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Rémy Bonnet. Variations du cycle hydrologique continental en France des années 1850 à aujourd'hui. Hydrologie. Université Paul Sabatier - Toulouse III, 2018. Français. ⟨NNT : 2018TOU30345⟩. ⟨tel-02479035⟩

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