Agriculture Reference
In-Depth Information
It has been estimated that the global cost of replacing water storage capacity lost to
sedimentation might be as much as $13 billion per year (World Bank 2007).
Because land management in upper catchments affects everyone else in a river
basin, policy makers tend to emphasize conservation goals for these areas. But,
catchments may also be home to large numbers of poor people. In some parts of
the world, upper catchment communities are often economically, politically, and
culturally marginalized, and their limited livelihood options center on the exploita-
tion of land, water, and forest resources. Equity considerations suggest that resource
management in upper catchments should allow for continued productive use of land,
water, and other resources by local communities, while also keeping in mind the
interests of downstream populations (Harrington et al. 2006).
Like water scarcity, land degradation demonstrates substantial spatial variability.
Land degradation in the form of erosion is usually more serious on sloping lands
such as are found in the foothills of the Himalayas; sloping areas in the Andes,
southern China, and Southeast Asia; rangelands in Africa and Central and West
Asia; and the semiarid lands of the Sahel. Pressure to farm hillsides and other mar-
ginal areas is reduced when agricultural productivity and employment are increased
in favored production areas.
Favored, intensively farmed agricultural areas are not immune from land degra-
dation. Here, however, it is not a result of erosion, but rather detrimental soil chemi-
cal, physical, and biological processes associated with unwise use of fertilizers and
pesticides, excessive tillage, unsuitable rotations, and inappropriate water manage-
ment practices. These factors threaten sustainable food production just as much as
soil loss from a hillside field—perhaps moreso given the heavy reliance placed on
these favored areas for maintaining global food security. Further information on soil
management and conservation is provided in Chapter 18.
clImAte chAnge
Climate change has recently come to be recognized as a serious threat to sustainable
food production. There are widespread concerns that climate change may under-
mine the capacity of agroecosystems to meet food needs. In addition, it may trigger
severe water shortages. Higher temperatures and the associated changes in hydro-
logical regimes may shorten growing seasons, increase the frequency of extreme and
destructive weather events, and shift the incidence of pests and diseases (Harrington
et al. 2006).
Analysis of multiple scenarios suggests that climate change will have serious
distributional impacts across countries, with poor countries in warm environments
suffering the most. Countries in low latitudes start with relatively high tempera-
tures. Further warming pushes these countries farther and farther away from optimal
temperatures for the production of climate-sensitive crops (Mendelsohn et al. 2006).
Even moderate warming in tropical countries (1 to 2°C) can significantly reduce
yields of crops (such as maize) that are already near the limit of their heat tolerance.
For temperature increases above 3°C, yield losses are likely to be widespread and
severe. Maize and wheat yields could decline by as much as 20 to 40% in parts of
sub-Saharan Africa, Central America, and tropical Asia (World Bank 2007).
