This is typically the driest region of West Africa. Not only are the rainfall amounts substantially less than in the coastal regions further south, the rainy season is also very short. Towards the end of the 20th century, rainfall deficits were observed more frequently. Future deviations of the mean precipitation from the 1901-1950 average are quite uncertain owing to divergence of model projections of 21st century precipitation anomalies. According to predictions from the GFDL CM2.0 and GFDL CM2.1 models the western Sahel should become drier in the future climate. The MIUB ECHO-G model on the other hand give an opposite indication. The remainder of the set of selected IPCC Fourth Assessment Report models do not indicate any possibility for a rainfall trend.
The models do not only over-predict the observed rainfall amounts in this driest area but also simulate too long a rainfall season, a mild exception being the MRI CGCM2.3 model. Such remarkable biases limit the confidence one can place on the model projected changes in rainfall amounts within the rainy season.