The Economics of Desertification, Land Degradation, and Drought

soils and higher land productivity. For example, the alluvial soils in the Nile, Ganges, and Mississippi
river deltas are results of long-term upstream soil erosion, and they all serve as breadbaskets in
riparian countries (Pimentel 2006). The provision of fertile sediment on floodplains may decrease
crop yield upstream while increasing yields in the alluvial valley plains (Pimentel 2006; Clark 1996).
The siltation of rivers and dams reduces reservoir water storage, leading to decreased water
availabilities for irrigation and for urban, industry, and hydroelectricity uses. It also damages
equipment and reduces flood control structures. Finally, it disrupts the stream ecology, decreases
navigability of waterways and harbors, increases maintenance costs of dams, and shortens the lifetime
of reservoirs. It is estimated that about 0.5 percent of annual water storage is lost annually due to
sedimentation from soil erosion (White 2010). At regional levels, reservoir storage losses are shown
in Figure 2.27. Central Asia experiences the largest annual loss of about 1 percent of storage capacity
due to siltation.
Figure 2.27—Annual loss of reservoir storage capacity due to sedimentation
% loss of storage capacity
South America
SSA
Southern Asia
Central Asia
Source: White 2010.
Note: SSA = Sub-Saharan Africa
0.1
0.23
0.52
0 0.2 0.4 0.6 0.8 1 1.2
If soil is wind eroded, it causes health problems, as soil particles that are propelled by strong
winds are abrasive and air pollutants. This can have an effect on health worldwide, as dust is
transported over long distances, leading to higher costs of healthcare (Montanarella 2007).
Furthermore, water quality can be influenced directly as concentrations of agrochemicals, metals, and
salts are increased. When biomass carbon in the soil is oxidized due to soil erosion and a loss of
biodiversity and biological activity, carbon dioxide is released into the atmosphere, contributing to
global warming. This action can be seen as a feedback mechanism, as global warming intensifies
rainfall, which in turn increases erosion (Pimentel 2006).
As a consequence of increased land degradation, other natural resources, such as lime for
neutralizing acidity or water for flushing irrigation salinity, are more in demand in order to repair the
land. This leads to off-site pollution and further losses of productivity and amenity values (Gretton
and Salma 1997).
Water pollution due to fertilizer use is also high. It is estimated that about 40 million tons of
nitrogen and 10 million tons of phosphorus are deposited into water bodies annually (Corcoran et al.
2010; Rockström et al. 2009). Nutrient runoff causes eutrophication in lakes and pollutes coral reefs,
leading to severe impacts on fish and human populations.
Further off-site effects refer to environmental services enjoyment of wild flora and fauna and
other human activities, such as recreation and the amenity value of water resources. As biodiversity
decreases, land becomes less resistant to droughts and requires more time to recover its productivity
(Pimentel 2006). The loss of keystone species might affect the survival of other species, as well as the
biological cycle within the ecosystem.
As the population grows, more food will be needed and more will be produced on marginal
lands with low productivity, which has an effect on food security as well as on farm income and
56
1
.