Modélisation pluie-débit et analyse du régime d'un bassin versant semi-aride sous influence nivale. Cas du bassin versant du Rheraya (Haut Atlas, Maroc)

River flow and groundwater recharge in the Marrakech region are closely linked to the hydrological dynamics in the High Atlas Mountains. To anticipate the effects of climate change in this area where the pressure on water resources is increasing, it is essential to quantify the contribution of snowmelt and rainfall to runoff. This study aims to modeling the runoff of the Rheraya River in the Moroccan High Atlas (225 km(2), elevations ranging between 1030 and 4165 m.a.s.l.) taking into account its snow component. For this purpose, the GR4J conceptual and lumped model was applied over the period 1989-2009, coupling it with the CemaNeige module for semi-distributed snow dynamics. This work allows for an improved characterization of the hydrologic regime of this watershed. The daily snow coverage simulated by CemaNeige is in good agreement with that extracted from the MODIS snow product in the period 2000-2009 (R-2 = 0,64). In addition, the simulated daily snow water equivalent is consistent with that measured at a weather station (2004-2006, R-2 = 0,81). Finally, the runoff simulation reproduces quite well the strong seasonal and inter-annual variability. However, the low Nash value obtained as compared to standards (0,45), can be linked to the low quality of runoff measurements (unstable riverbed). In conclusion, the hydrological regime of the Rheraya River is pluvio-nival with an unimodal distribution whose maximum in April is linked with snowmelt. It is at this time of the year that downstream populations are most vulnerable to the flow deficit because irrigated crops come into their growth period