A new look at hydrology in the Congo Basin, based on the study of
multi-decadal chronicles
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 both for 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, 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
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
since 1903. However, from the same year onwards, an increase in seasonal
variability and a decrease in spring flood flows can also be observed
for its bimodal tributaries. This article explains some of the
hydrological paradoxes specific to this basin, which illustrate the
complexity of its hydrological functioning. Finally, it 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 modelling are compared with those from in situ data.