Modelling the Impact of Small Dams on the Hydrological Re-Sponses of River Basins under Changing Climate Conditions: Case Study of the Faga Basin in Burkina-Faso

Abstract

In spite of its low emission of carbon dioxide Africa, specifically Sub-Saharan Africa is the most vulnerable to the effect of climate change. Many countries have already moved toward water scarcity and Burkina-Faso is part of the water stress countries. To supply the water requirements of increasing populations and to meet economic develop-ment needs, building small reservoirs seems to be a promising option for water resources development in Burkina-Faso. However, water storage infrastructures may seriously affect, among others, the river flow regime which could worsen under climate change condition. This study aims at assessing how small dams and/or climate change could impact river basin’s hydrology with the case study of the Faga River at Liptougou gauging station located in Burkina-Faso. For this purpose, hydrological parameters variation and climate extremes were assed in order to understand hydroclimatic behaviour over the basin throughout 1982-2010 using the indices of Nicholson combined to the Hanning filter and the non-parametric Mann-Kendall,Sen's slope test and RClimDex software with three climate stations and one hydrometric station data. Then we assessed the hydrological changes using the WaSiM hydrological modelled flow for the 1950-1958 as baseline for comparison and the EasyFit software. A field survey were per-formed to evaluate the environment and the socio-economic impact of small dams on down-stream communities We finally estimate the future changes of the river flow under increasing small dams and/or change climate scenarios over the 2040-2070. Three GCMs’ runs under RCP4.5 and RCP8.5 and 15% to 25% increase of dams’ number scenarios were used to run the WaSiM model. Results showed that annual precipitation increased by 18%. flow and potential evapotranspi-ration slightly increased of 3.48mm and 1.08mm respectively through 1982 2010 while annual mean temperature increased by 0.050C. Model simulation under RCP 4.5 showed a decrease flow of about 10.6% and 16.3% for RCP 8.5 for Can_ESM2 while EC-EARTH model simulations under RCP 4.5 and RCP 8.5 showed that the interannual flow will increase by about 4.9 and 8.1 respectively along 2040-2070. The simulation results showed that future increase in dams’ number could reduce the inter-annual river flow by about 37.40% to 40.03% using 15% and 25% increasing dams’ scenarios respectively. Combined dams and climate scenarios, under RCP 4.5 showed an interannual flow decrease of 3.75% for EC_EARTH and 32.8% for MPI_ESM. A decrease of 3.70 to 32.80% is observed for the total flow. RCP8.5 run show a surface runoff decrease of 22.1% with Can_ESM2 while MPI_ESM showed a baseflow decrease of 47.11% throughout 2040-2070.