Having verified the decrease in surface water resources observed over the last twenty years in West Africa, changes planned for the Sassandra basin, Côte d'Ivoire, are described. The methods used to generate two hundred year data series, the basis of previous studies, are presented. The generated time series allow the development of long term working patterns for cases similar to the climatic conditions pertaining before and since the drought of the late 1960s. The results demonstrate a clear drop in the performance of the water system, related to climatic conditions experienced since the start of the drought. The conclusions drawn from the comparisons and analyses indicate that, if the present conditions were to persist in West Africa, surface water resources would no longer meet needs which were identified and planned for on the basis of data records presenting characteristics different from those currently observed. The frequency of failures would then become much greater, leading to a serious decline in the output of existing facilities. Modifications made to the operation of the Buyo reservoir are also analysed.