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.

► A record of millennial scale hydrological changes in Sahara/Sahel during the Holocene.
► A time lag between the hydrological optimum and the maximum of NH insolation.
► Role of the groundwaters in the distribution and importance of water bodies.
► Role of the central massifs in supplying fresh waters to the lowlands.
► Evidence for a distinct E–W dynamics at the onset and the termination of the Holocene.