Modeling the impact of 1.5 and 2.0◦C global warming on the hydrology of the Faleme river basin (West Africa)

Climate change raises many questions about the future availability of water resources in West Africa. Indeed, water in this region is a fundamental element for many socio-economic activities. This study proposes an assessment of the impact of climate change on the hydrology of the Faleme basin, located in the Sahel (West Africa). The applied methodology consists in calibrating and validating the hydrological model GR4J before simulating the future evolution of flows in this catchment under of 1.5 and 2°C global warming.  Observed rainfall, potential evapotranspiration (PET), and river flows were used for calibration and validation of the GR4J model. Furthermore, output of three regional climate models (DMI-HIRHAM, SHIM-RCA, and BCCR-WRF) were bias corrected with the cumulative distribution function-transform (CDF-t) before used as input to the GR4J hydrological model to simulate future flows at the watershed scale. During the historical period the results shows a good correspondence between the simulated flows and those observed during calibration and validation, with Nash–Sutcliffe efficiencies (NSE) greater than 70%. Projections show a general increase in mean annual temperature and PET; a decrease in mean annual rainfall is projected by the DMI-HIRHAM, BCCR-WRF models and the overall mean; while a slight increase is noted with the SMHI-RCA model. As for future flows, a downward trend in annual and monthly average flows is expected in the two sub-basins of the Faleme (Kidira and Gourbassi) with input from the DMI-HIRHAM, BCCR-WRF models and the overall mean; however,  the GR4J forced by the SMHI-RCA model output, project increased flows. Furthermore, the decrease is more pronounced at Gourbassi sub-basin than at Kidira sub-basin. Thus, recommendations were made to mitigate the likely impacts of climate change on socio-economic activities that use water resources.