Environmental Changes on the Southern Sides of Lake Chad (1951-1987) Variations of the Lake Chad Lake Chad spans parts of Chad, Niger, Nigeria and Cameroon, between 12°n and 14°n and 13°E and 15°E. Highest level is at 283 meters but this has not been reached since the mid-1960. From then until 1973 there was an annual reduction in level but this has risen noticeably since 1995. The large variations in the Lake levels as a function of inflow from the Chari, from evaporation, and from infiltration cause changes in the lake ecosystem and thus influence human activity in respect of agriculture , livestock production and fishing. Lake Chad is located in a closed basin. There is no surface outlet and its level depends on the balance between inflow from the rivers and direct rainfall on the one hand evaporation and small infiltration losses to the ground water table on the other. The main catchment area is to the south of the lake in a zone swept over by the Inter-tropical Convergence Zone. The lake is thus greatly affected by variations in the ITCZ and reflects such variations that is why it is very important to state clearly the period under consideration or the state of the lake. Great variety and large seasonal and annual variations characterize the surface water resources of the Lake Chad and is Conventional Basin. Lake Chad is a shallow water body. Its characteristics are intimately related to the hydrological conditions, especially to the considerable year to year variation of the water level. The lake can be divided into a southern and nothern basin, these being separated by a ridge, known as the « Grande Barrière », between Baga Kawa and Baga Sola. Both basins where distinct in 1910 and 1928 (Tilho, 1928) and then again from 1974. (fig. n° 2 )  fig n°2 : Les grandes zones écologiques du Lac Tchad « normal », d’après Carmouze et al 1972 Phytogeographic domains Two phytogeographic domains : the sahelian and the soudanian ones, share the Lake Chad Basin area.The phytogeographic zonage of the vegetation was identificated by TROCHAIN (1970) . After the drought, the boundaries were revised (Gaston, 1981). (carte n°3 ). We can see on this figure that the southern sides of the lake Chad are at the intersection between the sahelo-saharian sector and the sahelo-soudanian sector.  Carte n°3 : Zonation phytogéographique du Bassin du Lac Tchad (d’après TROCHAIN, 1970, adapté par Gaston) |