Résumé
This chapter describes the variability of rainfall and river discharges in the Ogooué River Basin (ORB) in recent decades (since 1940). Due to its location crossing the Equator, the ORB receives abundant precipitation, which maintains one of the world's best‐preserved ecosystems. In contrast to neighboring forest basins that have been severely degraded because of deforestation, mining resource extraction, extension of agricultural areas, and river transport, which is a crucial alternative to the cruel lack of road infrastructures, the ORB is experimenting with an exceptional conservation policy in the region. For example, the rural penetration rate in Gabon is about 1 inhabitant per km
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and many studies report a deforestation rate close to 0%, with even full natural regeneration. However, the fluctuations of the standardized anomaly index of rainfall in the ORB show three main phases of variations: the first wet phase was characterized by abundant precipitations from 1940 to 1970, the second phase of long‐term mild drought was extended in 1970s and 1980s, and the final third phase presented a slight return of abundance in precipitation. Even though drought severity in the ORB was mainly weak, its effects in river discharges were very sensitive in seasonal and interannual scales. The pure equatorial regime of the ORB, characterized by equal maximum floods in spring and autumn, changed significantly from the difference between both maximum discharges of 13.5% during the 1960s to 27.0%, 38.4%, 33.9%, and 26.7% for the 1970s, 1980s, 2000s, and 2010s, respectively. A brief comparison between the ORB and the Congo River Basin showed that changes in the ORB are part of a regional process that Central Africa is undergoing with some spatial heterogeneities.