The study of the character of rainfall in the Sanaga basin (133.000 km2) in Cameroon between 1950 and 2008 from monthly data obtained from 10 rainfall stations, show a generalized decrease of mean annual rainfall during the deficitory period. This decrease is about 66 mm with a reoccurrence in dry stations from 1977-1978, accompanied by a decrease of 20 days of rainfall yearly at the Edea station between 1983 and 2007 in response to the recent dryness occurring in West and Central Africa. Spatially, there is a SSW longitudinal tilting/sliding of mean interannual isohyets during this deficitory phase, quite common in the North of the Basin (about 150-200 km) above the zones where the main dams are located, as against 50 km in the South. This shows the important role that forests play in regulating rainfall partterns. This is also explained by the intensification of aridification in the northern part of the country, intensification of the convection of the ITCZ over the reliefs and to more local circulations, temperature variations at the surface of the Atlantic Ocean, and a modification of free convection above the equatorial forest due to deforestation.