ABSTRACT
The basin has low relief in general, with altitudes varying between 1 and 920m. Mean altitude is about 257m, with more than half of the basin in the range of 200 to 300m. Rainfall follows a north-south gradient, with higher rainfall in the south and lower rainfall in the north. Average long-term annual rainfall varies from about 1600mm/a in the south-eastern part of the basin in Ghana to about 360mm/a in the northern part of Burkina Faso. Rainfall variability is very large during the rainy season and the onset of the rainy season is particularly unpredictable (UNEP-GEF Volta Project, 2013).
