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GEO: Global Environment Outlook
Global overview
The total
volume of water on Earth is about 1 400 million km3 of which
only 2.5 per cent, or about 35 million km3, is freshwater (see
table below). Most freshwater occurs in the form of permanent ice or snow,
locked up in Antarctica and Greenland, or in deep groundwater aquifers.
The principal sources of water for human use are lakes, rivers, soil
moisture and relatively shallow groundwater basins. The usable portion of
these sources is only about 200 000 km3 of water � less than 1
per cent of all freshwater and only 0.01 per cent of all water on Earth.
Much of this available water is located far from human populations,
further complicating issues of water use.
The
replenishment of freshwater depends on evaporation from the surface of the
oceans. About 505 000 km3, or a layer 1.4 metres thick,
evaporates from the oceans annually. Another 72 000 km3
evaporates from the land. About 80 per cent of all precipitation, or about
458 000 km3/year, falls on the oceans and the remaining 119 000
km3/year on land. The difference between precipitation on land
surfaces and evaporation from those surfaces (119 000 km3 minus
72 000 km3 annually) is run-off and groundwater recharge �
approximately 47 000 km3 annually (Gleick 1993). The figure
opposite shows one estimate of the average annual water balance of major
continental areas, including precipitation, evaporation and run-off. More
than one-half of all run-off occurs in Asia and South America, and a large
fraction occurs in a single river, the Amazon, which carries more than 6
000 km3 of water a year (Shiklomanov 1999).
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Major stocks of water
|
| |
volume
(1 000 km3) |
% of
total water |
% of
total freshwater |
| Salt water |
|
|
|
| Oceans |
1 338 000 |
96.54 |
|
| Saline/brackish groundwater |
12 870 |
0.93 |
|
| Salt water lakes |
85 |
0.006 |
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| Inland waters |
|
|
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| Glaciers, permanent snow cover |
24 064 |
1.74 |
68.7 |
| Fresh groundwater |
10 530 |
0.76 |
30.06 |
| Ground ice, permafrost |
300 |
0.022 |
0.86 |
| Freshwater lakes |
91 |
0.007 |
0.26 |
| Soil moisture |
16.5 |
0.001 |
0.05 |
| Atmospheric water vapour |
12.9 |
0.001 |
0.04 |
| Marshes, wetlands* |
11.5 |
0.001 |
0.03 |
| Rivers |
2.12 |
0.0002 |
0.006 |
| Incorporated in biota* |
1.12 |
0.0001 |
0.003 |
| Total water |
1 386 000 |
100 |
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| Total freshwater |
35 029 |
|
100 |
| Source: Shiklomanov
1993 |
Notes: totals may not add exactly due to rounding
* Marshes, wetlands and water incorporated in biota are often mixed
salt and freshwater |
Freshwater: Asia and the Pacific
The Asia and the Pacific Region accounts
for about 36 per cent of global run-off. Even so, water scarcity and
pollution are key issues and the region has the lowest per capita
availability of freshwater: renewable water resources amounted to about 3
690 m3 per capita/year in mid-1999 for the 30 largest countries
in the region for which records are available (UNDP, UNEP, World Bank and
WRI 2000 and United Nations Population Division 2001).
In absolute terms, China, India and
Indonesia have the largest water resources, more than one-half of the
region�s total. Several countries, including Bangladesh, India, Pakistan
and the Republic of Korea, already suffer from water scarcity or water
stress. More will do so as populations and consumption increase.
Agriculture is the biggest consumer (86 per cent), with smaller amounts
going to industry (8 per cent) and domestic use (6 per cent) (compiled
from UNDP, UNEP, World Bank and WRI 2000).
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The Executive Summary of the UN World Water Development Report is
available online...
 Why Water is the Big
Issue
� at any given moment almost half the developing world's people are
sick from unsafe water and sanitation.
� lack of water supply and sanitation robs millions of dignity,
energy, and time.
� frequent disease is the main cause of poor growth and early death.
� for a third of the world the real environmental crisis is squalor,
smells and disease on the doorstep.
� half of the developing world�s hospital beds are occupied by
victims of unsafe water and poor sanitation.
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