Abstract
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 that maintains one of the world’s best-preserved
ecosystems. In contrast to neighboring forest basins that have been
severely degraded because of deforestation, mining resources extraction,
extensions 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 km² 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 the long-term mild
drought was extended in the 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 on seasonal and inter-annual 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.