Contribution of Lakes in Sustaining Greening of the Sahara during the Mid-Holocene

Abstract

Abstract. The contribution of lake-climate feedback 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. Such lake-climate feedback was caused by the cyclonic circulation response related to weakened African Easterly Jet and enhanced Tropical Easterly Jet. According to Budyko aridity index, the northwestern Sahara climate region shifted from hyper-arid to arid or semi-arid with lake expansion. Moreover, precipitation scarcity could be reduced by up to 13 % to sustain semi-humid conditions. Such lake-climate feedback alleviates the Sahara aridity but relies on lake positions in the monsoon regions. Our findings are promising for understanding the contribution of lakes to sustaining the Green Sahara.