Chad is a landlocked country in north central Africa, with a territory twice the size of Texas. Population densities range from 54 persons per square kilometer in southern zones to 0.1 persons in the vast northern desert region, itself larger than France. The population of the capital city of N'Djamena, situated at the confluence of the Chari and Logone Rivers, is representative of Chad’s ethnic and cultural diversity.
Chad has four bioclimatic zones. The northernmost Saharan Desert zone averages less than 200 mm (8") of rainfall annually. The central Sahelian zone receives between 200 and 600 mm (24") of 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 small Guinea zone, limited to Chad's southwestern tip, ranges between 1,000 and 1,200 mm (47").
The country's 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 Ouaddai 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, one of the most important wetlands on the continent and home to hundreds of species of fish and birds, shrank dramatically over 4 decades due to increased water use and inadequate rainfall. The lake, the second-largest in West Africa, covered 25,000 square kilometers in 1963 but had decreased to 1,350 square kilometers as of 2002. 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.
Reference: US State Department - updated January 6, 2012