Chad has four bioclimatic zones. The northernmost Saharan zone averages less than 200 mm (8") of rainfall annually. The sparse human population is largely nomadic, with some livestock, mostly small ruminants and camels. The central Sahelian zone receives between 200 and 600 mm (24") rainfall and has vegetation ranging from grass/shrub steppe to thorny, open savanna. The southern zone, often referred to as the Sudanian zone, receives between 600 and 1,000 mm (39"), with woodland savanna and deciduous forests for vegetation. Rainfall in the Guinea zone, located in Chadís southwestern tip, ranges between 1,000 and 1,200 mm (47").

The countryís topography is generally flat, with the elevation gradually rising as one moves north and east away from Lake Chad. The highest point in Chad is Emi Koussi, a mountain that rises 3,100 meters (10,200 ft.) in the northern Tibesti Mountains. The Ennedi Plateau and the OuaddaÔ highlands in the east complete the image of a gradually sloping basin, which descends toward Lake Chad. There also are central highlands in the Guera region rising to 1,500 meters (4,900 ft.).

Lake Chad is the second-largest lake in West Africa and is one of the most important wetlands on the continent. Home to 120 species of fish and at least that many species of birds, the lake has shrunk dramatically in the last four decades due to the increased water use and low rainfall. Bordered by Chad, Niger, Nigeria, and Cameroon, Lake Chad currently covers only 1,350 square kilometers, down from 25,000 square kilometers in 1963. The Chari and Logone Rivers, both of which originate in the Central African Republic and flow northward, provide most of the water entering Lake Chad.