The concept of rainfall and streamflow normals in West and Central Africa in a context of climatic variability

This contribution to the debate on the revision of rainfall and streamflow normals concerns three countries of West Africa: Burkina Faso, Ivory Coast and Mali. The rainfall deficit (15-20% on average in the study area) and the river flow deficit (about 30-50% and sometimes more) observed over the past 30 years in West and Central Africa raise the problem of the reference period that must be considered in estimates of hydrological characteristics. The hypothesis of the concept of "normal" supporting these estimates is a stability of the climate. However, the effect of taking or not taking into account the data of recent years on the estimates of these characteristics can lead to very different results. This would have serious consequences for the development and management of water resources systems, as seen in two examples of dams.