Sahara and Sahel vulnerability to climate changes, lessons from Holocene hydrological data

The examination of more than 1500 paleohydrological dated records collected between 10 and 28°N during the last 50 years have been used to improve our knowledge and understanding of the Sahara and Sahel vulnerability to the Atlantic monsoon changes in the long-term. We have analyzed the distribution of water bodies (mainly lakes and wetlands) over time and space: the central Saharan massifs played a major role in favoring water supply to the lowlands throughout the whole African Humid Period. In addition, distinct East-West dynamics is recorded with humidity starting - and stopping - several millennia earlier to the east than to the west of the Sahara. A series of time lags are discussed: (1) between the maximum of deep (fresh water) lake formation during the early Holocene and the maximum of water body extensions during the mid-Holocene which highlight the primary role of aquifer water level in lake response to climate change (2) between the hydrological history of the Sahara and the Sahel and the forcings - mainly insolation changes - during the early and mid-Holocene which involves complex interactions between remnant ice sheet in the Northern Hemisphere, open water bodies in the Sahara and Sahel and the Atlantic monsoon system.