The humid soudanian zone includes the southern prefectures of Mayo-Kebbi, Tandjilé, Logone Occidental, Logone Oriental, Moyen-Chari, and southern Salamat. Between April and October, the rainy season brings between 750 and 1,250 millimeters of precipitation. Temperatures are high throughout the year. Daytime readings in Moundou, the major city in the southwest, range from 27° C in the middle of the cool season in January to about 40° C in the hot months of March, April, and May.

The soudanian region is predominantly savanna, or plains covered with a mixture of tropical or subtropical grasses and woodlands. The growth is lush during the rainy season but turns brown and dormant during the five-month dry season between November and March. Over a large part of the region, however, natural vegetation has yielded to agriculture.

Data as of December 1988