The Volta Basin is a climate-sensitive semi-arid to sub-humid region in West Africa. To investigate the impact of the expected global climate change on regional water availability, regional climate modelling was performed.

Two time slices (1991-2000 and 2030-2039) of the ECHAM4 scenario IS92a were dynamically downscaled with MM5 to a spatial resolution of 9 km. The quality of MM5 in reproducing regional climate was assessed using reanalysis data as initial and boundary conditions. Although an underestimation of rainfall in coastal areas was detected, sufficient accuracy in most parts of the Volta Basin could be achieved.

The regional climate simulations show an annual mean temperature increase by 1.2 to 1.3°C in the Volta Basin. This temperature change significantly exceeds inter-annual variability. A change in precipitation from -20% to +50% is simulated, with a mean increase of 5%.
In the rainy season rainfall predominantly increases, whereas a strong decrease is found for April, which is connected to a delay in the onset of the rainy season.
In addition, inter-annual variability in the Volta Basin increases in the early stage of the rainy season. The climate change signals in infiltration excess and evapotranspiration show a nonlinear response to precipitation change.
Aridity in the Volta Basin, expressed by the de Martonne aridity index, does not change significantly.
The change signal in precipitation predominantly lies within the range of inter-annual variability. In contrast, the decrease in April exceeds inter-annual variability in the Sahel region.

Person in Charge: Harald Kunstmann