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Because much of the world's surface water is far from concentrations
of human settlements, not all of it is readily usable.
- It is estimated that the freshwater available for human consumption
varies between 12 500 km3 and 14 000 km3
each year (Hinrichsen et al., 1998; Jackson et al., 2001).
- Many countries in Africa, the Middle East, Western Asia, and
some Eastern European countries have lower than average quantities
of freshwater resources available to their populations.
- Due to rapid population growth, the potential water availability
of Earth's population decreased from 12 900 m3 per
capita per year in 1970 to 9 000 m3 in 1990, and to
less than 7 000 m3 in 2000 (Clarke, 1991; Jackson et
al, 2001; Shiklomanov, 1999).
- In densely populated parts of Asia, Africa and Central and
Southern Europe, current per capita water availability is between
1 200 m3 and 5 000 m3 per year (Shiklomanov,
1999).
- The global availability of freshwater is projected to drop to
5 100 m3 per capita per year by 2025.
- This amount would be enough to meet individual human needs
if it were distributed equally among the world's population (Shiklomanov,
1999).
- It is estimated that 3 billion people will be in the water
scarcity category of 1 700 m3 per capita per year by
2025 (UNEP, 2002).
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The uneven distribution of freshwater creates major
problems of access and availability. For example:
- Asia and the Middle East are estimated to have 60% of the world's
population (~3 674 000 000 people in 2000), but only 36% of its
river runoff - much of which is confined to the short monsoon
season (Graphic Maps, 2001; Shiklomanov, 1999).
- South America, by contrast, has an estimated 6% of the global
population (~342 000 000 people in 2000) and 26% of its runoff
(Graphic Maps, 2001; Shiklomanov, 1999).
These examples do not take into account groundwater abstraction.
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