Historical Changes in Climate and Lake Chad Surface Area in the Chad Basin
Résumé
The Chad Basin has an area of about 2.5 Mkm2 and is considered the largest endoreic basin in the world. In the center of the basin is Lake Chad - a shallow lake (average ~1.5 m deep) with a surface area that has varied from ~25,000 km2 to ~2,000 km2 over the last 50 years. However, historically from Pleistocene to present time considerable changes in the surface area of the lake has occurred in response to climatic variability. During the Holocene (past ~12,000 yrs), the surface area of \textquotedblleftMegalake Chad\textquotedblright was estimated to have reached a maximum of ~340,000 km2 during the humid period 8500-6300 BP. Several periods of dramatic shrinkage of the Lake were also shown to have occurred, with for instance, an almost complete drying up of the Lake in the middle of the 15th century. Over the last century, instrumental records of hydrological data are available in the region, which show variability in both rainfall and surface water conditions.~ Present day shrinkage of the Lake was attributed to climatic variability and the induced environmental changes are accelerated by human demands on natural resources. Inter-basin surface water transfer is one option being canvassed to mitigate effects of the long-lasting shrinkage. However, because Lake Chad is an endoreic lake with no outflow to the ocean, the effect of injection of huge volume of water to its surface area needs to be fully understood. This is in order to minimise or avoid socio-economic impact that might have arise from excessive flooding of cultivated areas and/or villages, in addition to its impact on groundwater levels.