The Economics of Desertification, Land Degradation, and Drought

Figure 2.26—Impact of soil erosion on millet yield
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0.015
0.057
0.02 0.01
Source: Modified from den Biggelaar et al. 2003.
0.187
All theses mechanisms are closely interlinked and have spiral feedbacks on crop yields.
However, it is important to mention that the extent to which erosion actually reduces yields depends
on the types of crops, implying that the crop management system can have an influence on crop yields
and the effects of land degradation. In the long run and in instances of serious degradation, the effects
of land degradation might lead to temporary or permanent abandonment of plots and to a conversion
of land to lower-value uses (Scherr and Yadav 1996).
According to Bossio, Geheb, and Critchley (2010), there is a strong link between land and
water productivity, implying reduced water productivity due to land degradation, which leads to
greater demand for agricultural water. Water quality and storage may both be reduced due to land
degradation.
Socioeconomic on-site effects include the increase of production costs due to the need for
more inputs to address the negative physical impacts of land degradation. Income losses arise as a
consequence of erosion and land degradation, as farmers are not able to pay for inputs and to invest in
improved land management methods (Bojö 1996). These costs can be measured as productivity losses
through fertility and nutrient loss, soil loss through erosion, or a reduction in the vegetation cover—or
even as changes in groundwater supply, loss of wood production, loss of grazing and hunting
possibilities, carbon sequestration, nature conservation, and tourism.
Other ecosystem services are lost due to land degradation. For example, tree cutting reduces
the availability of fuelwood, which in turn increases the labor input required for collecting fuelwood
(Cooke et al. 2008). Degraded lands lead to loss of biodiversity, which in turn leads to reduction in
other ecosystem services used by households. Soil erosion reduces the absorptive and storage capacity
of water, which in turn increases the demand for water on eroded plots. Moderately eroded soils
absorb 7–44 percent less water per hectare per year from rainfall than do uneroded soils (Murphee and
McGregor 1991). An increase in the demand for irrigation water implies higher production costs, low
yields and plant biomass, and consequently lower overall species diversity within the farm ecosystem
(Walsh and Rowe 2001).
Overall, food security in particular is a major concern for households. Reduced land
productivity leads to food insecurity.
Off-Site Effects
Land degradation may also have important off-site costs and benefits, including the deposition of
large amounts of eroded soil in streams, lakes, and other ecosystems through soil sediments that are
transported in the surface water from eroded agricultural land into lake and river systems. The
deposits raise the waterways and make them more susceptible to overflowing and flooding; they also
contaminate the water with soil particles containing fertilizer and chemicals. The beneficial off-site
effects of soil erosion include the deposition of alluvial soils in the valley plains, which forms fertile
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0.29
0.011
Asia North America Africa Europe
yield loss per year (tons/ha per 1 cm topsoil lost) % yield loss
0.03
.