Earth Science

Drying Out

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Science  28 Apr 2006:
Vol. 312, Issue 5773, pp. 500
DOI: 10.1126/science.312.5773.500a

The semiarid Sahel region, which bridges the Sahara desert and the savanna landscape in Africa, has endured multiple extreme droughts since the 1960s. Loss of vegetation has been attributed in part to periods of reduced rainfall, but the long-term contribution of livestock grazing to local desertification is still debated. Recent studies have interpreted satellite data to support a greening process, or recovery of vegetation, since rainfall began to increase in the mid-1980s, suggesting that grazing has had minimal lasting impact on the landscape.

Hein and De Ridder argue that the satellite images have been systematically misinterpreted because of a flawed core assumption that rainfall variation would not alter rain-use efficiency (RUE): the ratio of annually generated plant material to rainfall. By analyzing data from six semiarid sites, they find that RUE instead appears to vary quadratically with rainfall. Correcting for this phenomenon suggests that anthropogenic degradation of the Sahel vegetation cover is a likely factor in the magnitude of the droughts over the past 40 years and suggests that future droughts may have a stronger impact than previously projected. — HJS

Global Change Biol. 12, 10.1111/j.1365-2486.2006.01135x (2006).

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