Abstract
The latest work on the main African rivers on the Atlantic coast has made it possible to subdivide the multi-year streamflow records into several homogeneous phases. The year 1970 seems to mark, for both West and Central Africa, the major hydroclimatic event of the 20th century, heralding its main period of deficit flow. For the first time, this article presents a comparative study of the hydro-rainfall records of five drainage systems (those of the Congo River and its main tributaries: Lualaba, Kasai, Sangha, and Oubangui) based on field data obtained on both the left and right banks of the Congo River. A reconstitution of the Cuvette Centrale regime is proposed. The 1970 hydro-rainfall disruption is common in most tributaries of the Congo River Basin, with significant reductions in flows depending on various factors (geographical location, vegetation cover, surface conditions and land use, etc.). The Oubangui River is the most fragile northern tributary that continues to suffer from flow deficits, with an increase in the duration and intensity of its low flows. Since 1995, flows of the Congo River at its main station in Brazzaville/Kinshasa seem to have returned to the interannual average of 1903. However, from 1995 onwards, an increase in seasonal variability and a decrease in spring flood flows can also be observed for bimodal tributaries of the Congo River. This article explains some of the hydrological paradoxes specific to this basin, which illustrate the complexity of its hydrological functioning. Finally, the study shows that the period of excess flow in the 1960s is the major hydrological anomaly of the Congo River over a continuous 116-year history. For the whole basin, hydrological variations are attenuated compared to those of precipitation. Finally, the hydrometric regimes reconstructed by spatial altimetry and modeling are compared with those from in situ data.