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Three key actions in the hydrologocal cycle:
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| Large clouds, such as towering cumulonimbus clouds, can keep droplets aloft longer, giving the droplets more chances to collide with other dropsÑthus producing larger raindrops! |
Precipitation:
As moisture droplets continue to cool, they coalesce around condensation nuclei
(dust, soot, etc.) to form water droplets, or raindrops. The largest of the
raindrops fall, colliding and merging with other droplets to form even larger
drops. Gradually, the drops become too heavy for the cloud's air circulation
to keep them aloft, and rainfall begins.
How does it all fit together?
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here.
What happens if you change one of the key actions?
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Evaporation:
Water evaporates from oceans, lakes and rivers. Oceans account for 97%
of the earth's water, so the majority (about 86%) of evaporation occurs
from them. 
Condensation: As water vapor rises, it cools in the upper atmosphere
and condenses into moisture droplets to form clouds. These moisture droplets
are a microscopic .002 cm in diameter—one raindrop is made of a million
or more moisture droplets! 