Climatic Variability and Hydrological Impacts in West Africa: Case of the Gambia Watershed (Senegal)

Since the 1970s, West African rivers have undergone profound changes related to the rainfall deficit and have led to a sharp decline in water resources. In the framework of mitigation and adaptation to the consequences of these changes among which, there is sometimes the scarcity of water resources (desertification and drought), sometimes the event of the important precipitations at the origin of the recurring floods, it is necessary to have a detailed knowledge of the impact of these upheavals on the flows of a basin. This study aims to analyze changes induced by rainfall variability on hydrological behavior of Gambia river basin from to Senegal. Climatological data (rainfall, temperature) of six selected stations in the Senegalese part of Gambia river basin for period 1960-2016 are used. To carry out study, methodology consisted on the one hand in determination of hydrological parameters (such as rainfall effective, runoff potential and infiltration potential) and on the other hand in the calculation of standard standardization index and the application of two tests (Pettitt rupture test and Mann Kendall trend test) to the series of hydrological parameters determined. The main results obtained made it possible to identify the manifestations of hydrological variability observed in Gambia river basin in Senegal. The different hydrological parameters analyzed vary over the years and describe a downward trend marked by a very significant rupture in 1970. The hydrological deficits evaluated are of order of -14.2% for average rainfall, -27 % for rainfall effective, -49.8% for runoff potential and -11.4% for infiltration potential. The decline in rainfall has, of course, consequences for the availability of water resources in river basin that is also vital