A Sahel lake that once spanned 28,000 square kilometres
Lake Chad sits where Nigeria, Niger, Chad, and Cameroon meet, draining a catchment larger than a million square kilometres. Nineteenth-century travelers still saw about 28,000 square kilometres of water; climate shifts and withdrawals have since rewritten the shoreline year by year.
The Chari and its Logone tributaries deliver most inflow from the Adamawa Plateau, with the Yobe adding from the west. Together the Chari and Logone bring about 95 percent of the inflow, while the Yobe manages under 2.5 percent. Water also seeps underground toward the Bodélé Depression about 480 kilometres to the north-east, and that hidden drainage carries salt away, so the south-west stays fresh and the north-east only slightly brackish. A shallow sill called the Great Barrier divides deeper southern waters from a lower northern basin; when southern levels top about 279 metres, water spills north. Mean annual rain near the lake is only about 330 millimetres, so evaporation rules the budget of this endorheic wetland.
The basin itself formed as the African Shield sagged, and its Precambrian floor lies beneath more than 3,600 metres of sediment. Between 39,000 BCE and 300 BCE the lake swelled four times into what geologists call Mega-Chad, over 180 metres deep and about 400,000 square kilometres in extent, spilling via the Mayo Kébbi and Benue toward the Atlantic.
During the African humid period fishers settled the shores and Nilo-Saharan peoples moved in. A pottery culture called Gajiganna appeared by 1800 BCE and was living in lakeside hamlets from about 1500 BCE, and some of the oldest domesticated pearl millet in West Africa turns up here. Permanent southern villages appear by 500 BCE beside Sao remains; Ptolemy already knew the lake by the mid-second century. Around 900 CE Kanuri-speaking Kanem founded an empire on the northeast shore. Berlin Conference borders later sliced the basin among colonial powers after 1884–85.
In 1870 the lake reached about 28,000 square kilometres and could overflow through the Bahr el-Ghazal. Drought from the late 1960s hit hardest in 1972 and 1984, and afterwards open water hovered between 2,000 and 5,000 square kilometres, with overgrazing, deforestation and irrigation diversions blamed alongside shifting rainfall.
Source: Lake Chad
