Hydrological
Cycle
85% of water vapor in atmosphere evaporates
from oceans.
About 50% of
precipitation that falls over land is runoff, 
and the other 50% is
transpired/evaporated.Water vapor molecules reside in atmosphere
for one week.
Ahrens
Fig. 4.1
85%
15%
50%
50%
Ultimate source of
all fresh water