Water, used by households,
agriculture, and industry, is clearly the most important good provided
by freshwater systems. Humans now withdraw about one fifth of the
worlds rivers base flow (the dry-weather flow or the
amount of available water in rivers most of the time), but in river
basins in arid or populous regions the proportion can be much higher.
This has implications for the species living in or dependent on
these systems, as well as for human water supplies. Between 1900
and 1995, withdrawals increased by a factor of more than six, which
is greater than twice the rate of population growth (WMO 1997).
Water supplies are distributed
unevenly around the world, with some areas containing abundant water
and others a much more limited supply. In water basins with high
water demand relative to the available runoff, water scarcity is
a growing problem. Many experts, governments, and international
organizations are predicting that water availability will be one
of the major challenges facing human society in the 21st century
and that the lack of water will be one of the key factors limiting
development (WMO 1997).
These maps show water
supply per person for individual river basins as of 1995 and projections
for 2025. Water experts define areas where per capita water supply
drops below 1,700 m3/year as experiencing water stressa
situation in which disruptive water shortages can frequently occur.
In areas where annual water supplies drop below 1,000 m3 per person
per year, the consequences can be more severe and lead to problems
with food production and economic development unless the region
is wealthy enough to apply new technologies for water use, conservation,
or reuse. This map is based on the analysis carried out by WRI for
the Pilot Analysis of Global Ecosystems: Freshwater Systems (PAGE).
The first map shows that as of 1995, some 41 percent of the worlds
population, or 2.3 billion people, live in river basins under water
stress, with per capita water supply below 1,700 m3/year. Of these,
some 1.7 billion people reside in highly stressed river basins where
water supply falls below 1,000 m3/year
In the second map we
see water scarcity projections for 2025. The analysis shows that
by 2025, assuming current consumption patterns continue, at least
3.5 billion people or 48 percent of the worlds projected
population will live in water-stressed river basins. Of these,
2.4 billion will live under high water stress conditions. This per
capita water supply calculation, however, does not take into account
the coping capabilities of different countries to deal with water
shortages. For example, high-income countries that are water scarce
may be able to cope to some degree with water shortages by investing
in desalination or reclaimed wastewater. The study also discounts
the use of fossil water sources because such use is unsustainable
in the long term.
In the second map, a
selected number of basins have been outlined. These watersheds represent
basins that are in or approaching water scarcity and where the projected
population for 2025 is expected to be higher than 10 million. Six
of these basins including, the Volta, Nile, Tigris and Euphrates,
Narmada, and the Colorado River basin in the United States, will
go from having more than 1,700 m3 to less than 1,700 m3 of water
per capita per year. Another 29 basins will descend further into
scarcity by 2025, including the Jubba, Godavari, Indus, Tapti, Syr
Darya, Orange, Limpopo, Huang He, Seine, Balsas, and the Rio Grande.