International Activities Related to Dryland Degradation Assessment and Drought - Monitoring and Predicting Agricultural Drought: A Global Study - page 421

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In ternational Activities Related to Dryland
D egradation Assessment and Drought
E arly Warning
ASHBINDU SINGH

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Land degradation usually occurs on drylands (arid, semiarid, and dry sub-
humid areas). According to the United Nations Convention to Combat
Desertification held in Paris in 1994 (UNCCD, 1999), drylands are defined
as those lands (other than polar and subpolar regions) where the ratio of
annual precipitation to potential evapotranspiration falls within the range
of 0.05-0.65.
Land degradation causes reduction in the biological or economic pro-
ductivity of those lands that may support cropland, rangelands, forest,
and woodlands. Land degradation threatens culturally unique agropas-
toral and silvopastoral farming systems and nomadic and transhumance
systems. The consequences of land degradation are widespread poverty,
hunger, migration, and creation of a potential cycle of debt for the affected
populations.
Historical awareness of the land degradation was cited, mainly at the
local and regional scales, by Plato in the 4th century B.C. in the Mediter-
ranean region, and in Mesopotamia and China (WRI, 2001). The occur-
rence of the “dust bowl” in the United States during the 1930s affected
farms and agricultural productivity, and several famines and mass migra-
tions, especially in Africa during the 1970s, were important landmarks of
land degradation in the 20th century.
It is estimated that more than 33% of the earth's land surface and 2.6
billion people are affected by land degradation and desertification in more
than 100 countries. About 73% of rangelands in dryland areas and 47%
of marginal rain-fed croplands, together with a significant percentage of
irrigated croplands, are currently degraded (WRI, 2001). In sub-Saharan
Africa, land degradation is widespread (20-50% of the land) and affects
some 200 million people. This region experiences poverty and frequent
droughts on a scale not known anywhere else in the world. Land degrada-

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