地理漫步·世界地理英语30篇（4）
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The Sahel: A Transitional Zone Under Pressure
萨赫勒地区：承受压力的过渡地带
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The Sahel stretches across Africa just south of the Sahara Desert, from Senegal to Sudan.
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It marks a climatic transition where semi-arid grasslands meet arid desert conditions.
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Rainfall here is highly variable—some years bring floods, others cause severe drought.
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Pastoralists migrate seasonally with livestock, adapting to shifting pasture and water sources.
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Population growth and crop expansion have reduced natural vegetation cover since the 1970s.
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Desertification isn’t just sand advancing—it’s soil degradation and loss of biological crusts.
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Dams on the Niger River alter downstream flooding patterns essential for flood-recession farming.
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Acacia trees planted in agroforestry systems improve soil nitrogen and reduce wind erosion.
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Early-warning systems now combine satellite rainfall data with local pastoralist knowledge.
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Youth-led cooperatives restore degraded land using contour bunds and native seed banks.