Résumé
To anticipate the potential changes in water quantity available within the Rherhaya mountainous watershed (near to Marrakech), it’s important to know the evolution of this resource in relation with climate changes. In this study we use the GR4J model with a snow module with time series of precipitations and discharge (1989 - 2009). The model was calibrated and validated successfully over various periods. Then we used an ensemble of 5 regional climate models (RCM) provided by the Med-CORDEX program with a method of perturbation by quantiles to simulate future scenarios of flow predictions.The evaluation of the precipitations simulated by the RCMs models (RCM) shows a strong underestimation of ~50% but a good reproduction of the cycle for the temperatures. The future changes according to two scenarios RCP4.5 and RCP8.5 show a rise of the temperatures (+1.4°, +2.6° respectively) in conjunction with a decrease in total precipitation (-19%,- 31%). Concerning the hydrological modeling with GR4J, stable results are obtained for calibration and validation whatever the chosen period, with maximum bias of 15% in validation on the monthly flows. Flow forecasts (2049-2065) present a strong projected decrease in surface runoff (-30%, -60%) and significant drops of the snow-covered reservoir levels, related to the precipitation decrease and the temperature increase.