The Volta basin is a major West African river basin that drains an area of 407,000 km² into the Gulf of Guinea. It is situated in the sub-humid to semi-arid West African Savanna Zone, and shows distinct North-South gradients. With greater distance from the coast, aridity increases, the growing season becomes shorter, and rainfalls are more erratic.
Annual precipitation rates vary from 2,000 mm in the south, to 500 mm in the northern parts of the basin. Potential evaporation rates are high, ranging from 1,500 mm in the south to more than 2,500 mm in the north, and less than 10% of the precipitation becomes useable as river flow.
The basin is shared by six riparian countries, of which Burkina Faso (46%) and Ghana (39%) share the major portion, and the remaining 15% are shared by Togo (6%), Benin (4%), Mali (3%), and Cote d’Ivoire (2%) (Barry et al. 2006).
The most significant hydrological structure is the Akosombo Dam, which holds back the water of the White Volta, Black Volta, and the Oti for the generation of hydro-power. Its construction was completed in 1965 and formed Lake Volta, which is still the second largest (8,500 km2) man-made lake in the world today. The Akosombo Dam is of strategic importance to the economy of Ghana. It generates 80% of the power produced in the country.