IWRA Proceedings

AbstractAs in most of West and Central Africa, the rainfall regime over the Lake Chad basin has changed around 1970 from a humid to a dry period. Lake Chad being a closed lake, its surface area has changed according to the lower water inputs from the watershed. The lake, which covered about 22000 km2 in the 1960s, is now divided into different individual seasonal or perennial lake basins. In the northern basin of the lake, the seasonally inundated area has varied from zero in dry years (as in 1985, 1987, 1988) to 6000 km2 (1979, 1989, 2000 and 2001). In the southern basin of the lake, the between year variability has markedly decreased. The changes in lake area and in the links between the lake basins have been modelled as a function of the river inputs. Satellite estimates of water area in the northern basin and gauge levels in the southern basin have been used as calibration data. The water volumes incorporated in and lost by the sediments during the annual wet and dry cycle have been taken into account in the model. The hydrologic changes are the driving forces for the natural resources associated with the lake i.e. fisheries, recession cultivation on the lake floor and green vegetation for livestock. Whereas the yearly cycle of the natural resources has become fairly predictable in the southern basin, vulnerability has much increased in the northern basin. Field observations and the model are used to discuss the benefits and drawbacks of the present situation compared with the wet period before 1970, and in the hypothesis of climate change. The possible impact of the planned inter-basin transfers from the Congo-Zaire basin is also analyzed.