Estimates of global water resources based
on several different calculation methods have produced varied estimates.
Shiklomanov in Gleick (1993) estimated that:
- The total volume of water on Earth is ~1.4 billion km3.
- The volume of freshwater resources is ~35 million km3,
or about 2.5% of the total volume.
- Of these freshwater resources, ~24 million km3 or 68.9% is in
the form of ice and permanent snow cover in mountainous regions,
the Antarctic and Arctic regions.
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- Some 8 million km3 or 30.8% is stored underground
in the form of groundwater (shallow and deep groundwater basins
up to 2 000 metres, soil moisture, swamp water and permafrost).
This constitutes about 97% of all the freshwater that is potentially
available for human use.
- Freshwater lakes and rivers contain an estimated 105 000 km3
or ~0.3% of the world's freshwater.
- The total usable freshwater supply for ecosystems and humans
is ~200 000 km3 of water, which is < 1% of all freshwater
resources, and only 0.01% of all the water on Earth (Gleick, 1993;
Shiklomanov, 1999).
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