A 3,000-mile belt marks the slow-moving frontline of the Sahara's growth

The Sahel stretches from the Atlantic to the Red Sea as a semi-arid transition zone between the Sahara and the greener savannas to the south. Overgrazing and farming have stripped away vegetation holding the soil together, and the Sahara has crept roughly 10% further into the Sahel over just the past half-century.

— Wikipedia contributors, Sahel — Transition zone, Sahara-Sudanian savanna