地理漫步·世界地理英语30篇（4）

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萨赫勒地区：承受压力的过渡地带

The Sahel stretches across Africa just south of the Sahara Desert, from Senegal to Sudan.
It marks a climatic transition where semi-arid grasslands meet arid desert conditions.
Rainfall here is highly variable—some years bring floods, others cause severe drought.
Pastoralists migrate seasonally with livestock, adapting to shifting pasture and water sources.
Population growth and crop expansion have reduced natural vegetation cover since the 1970s.
Desertification isn’t just sand advancing—it’s soil degradation and loss of biological crusts.
Dams on the Niger River alter downstream flooding patterns essential for flood-recession farming.
Acacia trees planted in agroforestry systems improve soil nitrogen and reduce wind erosion.
Early-warning systems now combine satellite rainfall data with local pastoralist knowledge.
Youth-led cooperatives restore degraded land using contour bunds and native seed banks.