Lake Chad

The Lake Chad Basin (LCB) is an intracratonic structure that dates from the Phanerozoic and is located in central Africa, at the northernmost boundary of the semi-arid Sahel belt and south of the Sahara desert. The LCB is one of the largest endorheic basins in the world, with a theoretical hydrologic basin surface of 2.500.000 km². Lake Chad lies in the path of the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), which makes it ideally situated to study summer monsoon variability in West Africa through time. While over 80% of the water input to the lake comes from the Chari-Logone River system that drains water from the tropical Savannah in the south, the remaining 20% of water input enters from direct rainfall on this hydrologic basin and from the Komadougou Yobe River system in the west. The water output from this endorheic basin is mainly through evaporation (95%) and the remaining water (5%) is lost through lake-floor seepage.

The LCB can be divided into two sub-basins, one in the south and one in the north. The present-day Lake Chad has a water depth of only 3 m and occupies the southern sub-basin, while the northern sub-basin is presently dry it has filled up with water in the past during intense rainy seasons. These sub basins are linked by the hyper-arid Bahr el Ghazal valley with an elevation of 285 m above mean sea level (AMSL). Yet the two basins where connected during the middle-Holocene humid period forming the Lake Mega-Chad that covered over 350.000 km², an area 25 times larger than today with a maximum depth of 170 m. Indeed, despite previous studies, little is known about the timing and amplitude of lake level fluctuations. So far, the estimation of its maximum extension only offers a static view of the early and mid-Holocene Lake Chad, while centennial lake level variations have also been highlighted.

Leading PI: Dr. Florence Sylvestre (CEREGE, Aix en Provence, France)