Environmental Changes on the Southern Sides of Lake Chad (1951-1987) Diane Brami Laboratoire Prodig, CNRS Paris 1-Paris 4 -Paris 7 Ephe France Email: dianebrami@club-internet.fr Location The Lake Chad Basin which lyes between the 8th N and the 16th N parallels of latitude comes under a tropical climate with unimodal rainfall. The rains occur within the boreal summer, their maximum is in august. In the northern side of the 16th parallel the rainy season lasts two or three months, whereas in the south it can last six months. During the two last decades the rains were disminishing (carte n° 1).  Carte n° 1 : Position des isohyètes avant et après la sécheresse, agrhymet, Morel 1992 In the Chad basin and in particular on the southern sides of lake Chad (Chad), the natural environment is organized according to hydrometric and pluviometric conditions. The morphology induces a zoned organization of the plant covering whose little diversified species cover vast homogeneous areas which are comparatively easy to inventory . The balance of this natural environment is dependent upon not only rainfall but also the inputs of the rivers Logone and Chari (carte n° 2).  Carte n°2 : Carte de situation : Bassin conventionnel avec les lacs et les fleuves ainsi que les zones inondables The rivers Chari and Logone The major rivers are the Chari and its tributary the Logone, they have a tropical transition type of regime characterized by a main annual flow and a low flow the rest of the year (fig. n°1).  fig. n°1 : Les débits mensuels du Chari à N’Djaména. Comparaison entre la période 1932-1972 et la période de sécheresse 1972-1992
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