tee, USSR, 1974). Although this may appear to be an enormous volume of water, 9
7% of it is sea water containing 3% of salt. This means that, as shown in Figur
e I , many terrestrial animals and plants as well as humankinds and its society
is dependent on freshwater comprising only 3% of all water on the planet.
It can be seen here that freshwater accounts for only a little less than 3% of
all the water that exists on earth. Moreover, 70% of this is fixed in the form
of glacier in Antarctica, Greenland and high altitude regions and nearly 30% is
stored in the soil layer and perma-frost. The water stored in rivers and lakes
that supports the existence of humankinds accounts for a mere 0.51% of all fre
shwater (35 X 106km3) on earth. The volume of vapor in atmosphere that feeds an
enormous amount of precipitation accounts for only 0.04% of all freshwater and
corresponds to a depth of 25mm if used to cover the planet. The amount of wate
r that exists in the atmosphere can only provide 10 days of rainfall. Then wher
e docs the precipitation for the remaining 355 days come from?
To answer this question, we must look at the circulation of water that takes pl
ace between the ocean, atmosphere and land by using solar radiation that enters
the earth after travel-ling 150 million kilometers from the sun as source of e
nergy. Its process is shown in
