Recent Budget of Hydroclimatology and Hydrosedimentology of the Congo River in Central Africa

Although the Congo Basin is still one of the least studied river basins in the world, this paper attempts to provide a multidisciplinary but non-exhaustive synthesis on the general hydrology of the Congo River by highlighting some points of interest and some particular results obtained over a century of surveys and scientific studies. The Congo River is especially marked by its hydrological regularity only interrupted by the wet decade of 1960, which is its major anomaly over nearly 120 years of daily observations. Its interannual flow is 40,500 m3 s−1. This great flow regularity should not hide important spatial variations. As an example, we can cite the Ubangi basin, which is the most northern and the most affected by a reduction in flow, which has been a cause for concern since 1970 and constitutes a serious hindrance for river navigation. With regard to material fluxes, nearly 88 × 106 tonnes of material are exported annually from the Congo Basin to the Atlantic Ocean, composed of 33.6 × 106 tonnes of TSS, 38.1 × 106 tonnes of TDS and 16.2 × 106 tonnes of DOC. In this ancient flat basin, the absence of mountains chains and the extent of its coverage by dense rainforest explains that chemical weathering (10.6 t km−2 year−1 of TDS) slightly predominates physical erosion (9.3 t km−2 year−1 of TSS), followed by organic production (4.5 t km−2 year−1 of DOC). As the interannual mean discharges are similar, it can be assumed that these interannual averages of material fluxes, calculated over the longest period (2006–2017) of monthly monitoring of its sedimentology and bio-physical-chemistry, are therefore representative of the flow record available since 1902 (with the exception of the wet decade of 1960). Spatial heterogeneity within the Congo Basin has made it possible to establish an original hydrological classification of right bank tributaries, which takes into account vegetation cover and lithology to explain their hydrological regimes. Those of the Batéké plateau present a hydroclimatic paradox with hydrological regimes that are among the most stable on the planet, but also with some of the most pristine waters as a result of the intense drainage of an immense sandy-sandstone aquifer. This aquifer contributes to the regularity of the Congo River flows, as does the buffer role of the mysterious “Cuvette Centrale”. As the study of this last one sector can only be done indirectly, this paper presents its first hydrological regime calculated by inter-gauging station water balance. Without neglecting the indispensable in situ work, the contributions of remote sensing and numerical modelling should be increasingly used to try to circumvent the dramatic lack of field data that persists in this basin

Wavelet Analysis on the Variability and the Teleconnectivity of the Rainfall of the Congo Basin for 1940 – 1999.

International audienceIt is known that the spatial and temporal variability’s of rainfall in the Congo Basin are complex because of its size, diversity of climates, topography, seasonal migration of the intertropical convergence zone (ITCZ), and the influence of oceans SST variations.This basin is characterized by low density of meteorological stations associated with a high percentage of missing data which is a high source of uncertainty for the results.However gridded database of rainfall (CRU, IRD,…) are available and can be used for various needs such as regional studies and modeling.We propose to quantify this variability using a wavelet analysis.Wavelet analysis of the Congo basin rainfall shows some energy bands:Annual fluctuations are the most representative and the most structured signal, explaining more than 30 % of the total rainfall variability;Multi-year fluctuations have a lower contribution (less than 10 %) during this period. It is clear that rainfall is highly structured by the annual cycle so that a transformation of rainfall data is requiredand allows to evidence the eventual connection of 2 to 8 and 8 to 16 years bands.We can observe three major shifts (around 1960, 1970 and 1983) in the signal (instationarities) of the rainfall in the Congo, Kasai and Oubangui basin’s, which affected the 2-4 years, 4-8 and the 8-16 bands.The wavelets coherence confirms a weak relationship between the rainfalls of the Congo basin and the Pacific and tropical Atlantic long term SST forcing

Hydroclimatogical Changes and Impacts on Seasonal Regimes of African Equatorial Rivers.

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