African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

The African Humid Period (similar to 11,000-5,000 years before present) was the most recent of several precessionally paced wet intervals during which an increase in the Northern Hemisphere summer incoming solar radiation intensifies the West African Monsoon leading to dramatic changes over northern Africa. However, insolation anomaly alone is not sufficient and feedbacks are essential for further amplification of the monsoon. The most significant feedbacks derive from the land surface, arising from changes to vegetation, soil properties, and distribution of surface water. We show that in contrast to previous studies that have explored the individual impacts of these feedbacks, a modern climate model yields a much greater increase in precipitation in response to their collective effect. Agreement with proxies is improved while the desert-steppe transition is pushed further northward than in any previous study. In the West African Sahel, intensities of summer daily mean and extreme precipitation increase by 150% and 90%, respectively.