Modelling the Spatial Variation of Hydrology in Volta River Basin of West Africa under Climate Change

Spatial variability in Volta basin’s climate coupled with climate change increases unpredictability and unreliability of rain-fed agriculture, putting livelihoods of the inhabitants under severe risk. Though there have been numerous studies on the hydrological response of the basin to climate change, only a few have dealt into its spatial variation. To fill up the existing gap, the spatial variation of hydrology of Volta basin under projected impacts of climate change is investigated using high resolution (0.3°~3 km) National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) data as observational data, Global Climate Model HadCM3, IPCC A1B emissions scenario and Soil, and Water Assessment Tool (SWAT). Calibration results from flow stations Dapola (R²=0.74, NSE=0.72), Nawuni (R²=0.86, NSE=0.88), and Bamboi (R²=0.82, NSE=0.80) show reasonable simulation of the basin’s hydrology, in general. Overall the simulation indicates higher spatial variability, with variability much higher at the end of the century (2071-2100). There is a greater average increase in rainfall and surface runoff in northern catchments compared to the south with average potential evapotranspiration and evapotranspiration much higher in southern catchments compared to the north. Contrary to projected increase in rainfall in the basin, some sub-basins in north and south show a decrease. Decrease ranges from 2% to 10%, whilst increase in surface runoff is in the range of 16% to 76% in some sub-basins is far greater than the basin-wide range of increase i.e., 9% to 14%. This might impact negatively on the rain-fed agriculture and also intensify flood events, respectively, in these sub-basins. There is, therefore, a call for a decentralized approach in the basin’s water resources management that incorporates the spatial variability of the hydrologic cycle into local climate change adaptation mechanisms.