Contribution of lakes in sustaining the Sahara greening during the mid-Holocene

Abstract

The climate impact contribution of lakes to sustain the Green Sahara in the mid-Holocene (MH, 6000 years ago) is still under debate. To assess the lake-induced climate response over North Africa, we investigated the roles of western Sahara lakes and Megalake Chad using reconstructions of MH Sahara lake maps as surface boundary conditions for the isotope-enabled atmospheric model MIROC5-iso. Our results show that the western Sahara lakes pushed the West African monsoon northward and extended it eastward by expanding Megalake Chad. This lake-climate impact was caused by the cyclonic circulation response related to the weakened African Easterly Jet and enhanced Tropical Easterly Jet. According to the Budyko aridity index, the northwestern Sahara climate region shifted from hyper-arid to arid or semi-arid with the lake expansion. Moreover, precipitation scarcity could have been reduced by up to 13 % to sustain the semi-humid conditions. Such lake-climate impacts could alleviate Sahara aridity, relying on lake positions in the monsoon regions. Our findings are promising for understanding the contribution of lakes to sustaining the Green Sahara.