Impacts of climate change on surface water resource availability in Alibori sub-watershed at the Yankin outlet (Northern Benin/West Africa)

Surface water resources are exposed to the effects of climate change, which poses a threat to agricultural activities in particular and socio-economic development in general. This study aims to characterize the effect of current and future climate change on surface water resource in the Alibori sub-watershed at the Yankin outlet. The historical data cover the period from 1965 to 2015 and include climate and hydrometric series respectively from the Meteo-Benin and the General Water Directorate databases. The simulation data are those of the HadGEM2-ES climate model under Representative Concentration Pathways (RCP) 4.5 and 8.5 for the horizons 2050 (time period 2041 - 2060) and 2070 (time period 2061 - 2080). These data were processed by descriptive statistics methods and the global conceptual hydrological model GR2M was used to evaluate the flow of the Alibori River for each climate scenario at the horizons 2050 and 2070. The results reveal two breaks in the flow series in 1970 and 1993, hence the consideration of the time periods 1965-1970, 1971-1993 and 1994-2015 for the analysis of current variations. Between the time periods 1965-1970 and 1971-1993, the rainfall decrease by 13% and the flow decrease by 55%. On the other hand, between the time periods 1971-1993 and 1994-2015, these two terms of the hydrological balance have experienced increases estimates at 7% for rainfull and 84% for flow, resulting in flooding phenomena that have become annual in recent decades in the sub-watershed. Similarly, by 2050 and 2070, and regardless of the RCP 4.5 or RCP8.5 scenario, the variations induced by climate change seriously affect the volume of runoff. There is a very significant increase in the average monthly flow, especially from July to October, while the annual hydrological pattern remains unchanged. Faced with this situation, appropriate strategies should be sought in conjunction with the local populations and authorities.

Keywords: Surface water resource, Climate change, Hydrological balance, Alibori sub-watershed at Yankin, Benin