The area falls within northern boundary of West African secondary rainfall maxima region, characterized by a prolonged rainy season. Decadal to multi-decadal rainfall fluctuations occurred during the 20th century with the last few years mainly wetter than average. There is some evidence that wetter-than-average seasons will dominate during much of the 21st century as projected by the CCCMA CGCM3.1 and MPI ECHAM5 models, and to a lesser extent by the MRI Mk3.0 model. The other models project a downward trend but this predicted shift in the mean is less significant.
Most models represent the observed 20th century annual cycle acceptably well albeit with an early and late season wet bias. The MIUB ECHO-G model simulate an unrealistic bimodal rainfall regime. The models which project an upward 21st century rainfall trend (e.g. the CCCMA CGCM3.1 and MPI ECHAM5 models) predict increased rainfall intensity during the peak rainfall months (August, September and October) in the future climate. The remainder of the models project a slight reduction in the amplitude of the annual cycle consistent with their predictions for a non-significant shift towards drier conditions in the future climate. There are no obvious indications of a likely change in the rainfall onset and cessation dates/months.