Spatiotemporal variations in hydrological regimes within Central Africa during the XXth century

Using several statistical tests, we divided into homogeneous segments the XXth century long discharges data series and the rainfall data series of the Congo River and of several of its right bank sub-catchments, These tests revealed that the River Congo at Brazzaville experienced a phase of so called stable discharge from the beginning of the XXth century until 1960, a phase of surplus discharge during the 1960s, testimony to its centennial flooding, and then from 1971 onwards, two successive phases of lower discharge. The second one, stretching from 1980 up to now, being the most accentuated with a 10% drop in the total series' interannual discharge (40 600 m(3) s(-1)). It has only been very recently, in 1990 that the river dropped to its lowest level of the century. The dates at which hydrological discontinuities appear, are observed to be globally similar within practically all of the tributaries studied, the most significant bring that of 1970, already well known in West Africa. During the second half of the century, these discontinuities occur roughly every ten years at the beginning of the 1960s, 1970s, and 1980s. Rainfall discontinuities are not as numerous as discharges ones. They separate homogeneous phases whose variations between them are less pronounced than that of those separated by discharges discontinuities. This underlines the major importance of the geographical location and of the physiographical characteristics of river basins on hydrological spatiotemporal variations. Lastly, we show that the effects of the recent drought are more visible and pronounced in the northern areas of this vast basin than in the southern ones. (C) 2001 Elsevier Science B.V. All rights reserved.