Wetlands of North Africa During the Mid-Holocene Were at Least Five Times the Area Today

The Sahara was significantly wetter and greener than today during the mid-Holocene (similar to 6,000 years before present), and those conditions were likely maintained by feedbacks from evaporating wetlands and riparian zones. A lack of spatially continuous wetland reconstruction is the major obstacle to investigating their impacts on climate and vegetation during that epoch. Here, we estimate high-resolution gridded wetland distribution up to 15 '' in the mid-Holocene North Africa obtained with three statistical and hydrological modeling approaches forced by enhanced and calibrated precipitation from climate models. These wetland models have good performance for present-day conditions and reproduce mid-Holocene hydrological elements evaluated by 297 paleo-records. Simulation results show that 18.9 4.0% of land surface in North Africa was covered by wetlands during the mid-Holocene. Our results highlight the impact of natural climate change on wetland areas and provide a data set for modeling studies to include wetland feedbacks. Plain Language Summary Several lines of evidence show that northern Africa was considerably wetter and greener than today at similar to 6,000 years ago, which is known as the mid-Holocene Green Sahara (GS). However, most current models could not reproduce climate in the GS. The importance of wetland feedbacks on sustaining a wetter climate has partially been recognized while large uncertainties in wetland coverage make it difficult to examine wetland feedbacks in climate models. We trained several wetland models under present climate and applied them to wetland reconstructions of GS. The produced wetland maps could capture dense wetlands indicated by 297 paleo-records. The total wetland fraction in the mid-Holocene North Africa is 18.9 4.0%, which is more than five times the area today (similar to 2.8%). The relationship between wetland fraction and precipitation is examined in our models. This work improves our understanding of the GS enigma, and has implications for potential greening and wetting of Sahel and Sahara in the future. Key Points We present high-resolution reconstructions of wetland distribution up to 15 '' for the mid-Holocene North Africa During the mid-Holocene, 18.9 +/- 4.0% of land surface in North Africa was covered by wetlands The relationship between precipitation and wetland fraction in the mid-Holocene Sahara is explored