Why was the Sahara wetter during the early Holocene?

During the early Holocene (approximately 11,700 to 6,000 years ago), the Sahara experienced a period of increased humidity and vegetation known as the African Humid Period. This transformation was primarily driven by orbital forcing, specifically changes in Earth’s precession, axial tilt, and eccentricity.12

These orbital changes resulted in higher solar radiation during the Northern Hemisphere summer—roughly 7 percent higher than today—which warmed the continental landmass. This heating created a low-pressure zone over North Africa, which "supercharged" the West African monsoon and the Indian Ocean monsoon, drawing moisture-laden air from the Atlantic and Indian Oceans deep into the continental interior.12

This process was further amplified by positive feedback loops involving the atmosphere, soil, and vegetation: increased rainfall led to lusher plant cover and wetter soils, which in turn enhanced moisture recycling and allowed the monsoon to penetrate further across the Sahara. As a result, the region was transformed into a landscape of grasslands, woodlands, and deep freshwater lakes, supporting diverse wildlife and human populations until decreasing summer insolation led to a gradual drying trend.213