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The Economics of Desertification, Land Degradation, and Drought

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Figure 2.12—Areas affected by human-induced l<strong>and</strong> degradation measured by a declining<br />

NDVI (Change in NDVI from 1982–2003 with a three-year base- <strong>and</strong> endline)<br />

Source: Vlek, Le, <strong>and</strong> Tamene 2010.<br />

To analyze the role <strong>of</strong> population as a factor influencing l<strong>and</strong> degradation, the authors used<br />

three classes <strong>of</strong> population density: low, high, <strong>and</strong> very high. Consistent with Bai et al (2008b), Vlek,<br />

Le, <strong>and</strong> Tamene (2010) found low population densities in areas most affected by degradation. <strong>The</strong>se<br />

areas may constitute marginal or fragile l<strong>and</strong>s with limited carrying capacity. In addition, in some<br />

areas, high population densities are associated with l<strong>and</strong> degradation on probably more fertile l<strong>and</strong>s.<br />

Examples <strong>of</strong> such areas are the densely populated areas in western Africa—especially the humid<br />

southwestern areas. In those areas, degradation problems could be addressed by improved access to<br />

fertilizer <strong>and</strong> erosion control measures. <strong>The</strong> authors also used FAO soil classes to assess whether soil<br />

<strong>and</strong> terrain constraints affect NDVI decline; they observed that 30 percent <strong>of</strong> the degraded areas relate<br />

to unsuitable agricultural soils. In addition, information on l<strong>and</strong> use can help explain the human<br />

impact by the l<strong>and</strong> use type <strong>of</strong> the degraded l<strong>and</strong>. Finally, the authors analyzed the pressure <strong>of</strong><br />

anthropogenic activities on l<strong>and</strong> using Human Appropriation <strong>of</strong> Net Primary Production (HANPP),<br />

which is the amount <strong>of</strong> NPP used by humans (for example, for harvested crops). <strong>The</strong> higher the<br />

HANPP (expressed as a percentage <strong>of</strong> NPP), the greater the human consumption or appropriation. For<br />

Sub-Saharan Africa, the average HANPP suggests a light human impact, though there is wide<br />

variability across countries. High values <strong>of</strong> HANPP are associated with areas known for food<br />

insecurity <strong>and</strong> may also reveal areas with future insecurity. This finding is consistent with Bai et al.<br />

(2008b), who observed a positive correlation between l<strong>and</strong> degradation <strong>and</strong> poverty. However, Bai et<br />

al (2008b) admitted that this study can only be seen as a way to locate global hot spots that appear to<br />

be threatened by human-induced l<strong>and</strong> degradation; further verification <strong>and</strong> analysis in the field would<br />

be needed. <strong>The</strong> coarse resolution <strong>of</strong> 8 kilometers may also hide improvement or degradation; finer<br />

resolution is required to give better estimates. This study is also only limited to Sub-Saharan Africa;<br />

future studies should provide analysis in other regions <strong>of</strong> the world.<br />

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