It's ironic that the wettest place
in the world manages to thirst
for water each winter when no
rain falls at all for months at a
time. The type of weather
phenomenon that brings so
much rain to this part of the
world is called the monsoons.
Monsoons are seasonal winds
that blow from one direction for
approximately six months,
bringing torrential rains, and
then blow from the opposite
direction for the remaining six
months, during which little rain
falls. During the wet season
moist air is cooled as it blows
over rising land, letting abundant
rain fall on the windward side of
mountain ranges. But because of
widespread destruction of
conifer forests that protected the
soil, the ground does not absorb
the rain that falls so heavily
during the monsoon season. The
city of Cherrapunji is 1,290
meters above sea level and
much of the torrential rains run
off the mountains into the
valley below, which receives an
annual rainfall of 1,270
centimeters. Once it rained
2,290 centimeters in one
season! The irrigation system for
the town of Cherrapunji is
insufficient to provide adequate
amounts of clean, potable water
from below during the dry
season. People who live there
frequently have to travel on foot
for several kilometers to bathe
and get drinking water.
What Causes so much Rainfall?
The oceans are the chief source
of rain, but lakes and rivers also
contribute to it. The sun's heat
evaporates the water. It remains
in the atmosphere as an invisible
vapor until it condenses, first into
clouds and then into raindrops.
Condensation happens when the
air is cooled. For raindrops to
form there must be particulate
matter in the air, such as dust or
salt, at temperatures above
freezing. These particles are
called condensation nuclei.
When the nuclei are cooled to
temperatures below the freezing
point, water condenses around
them in layers. The particles
become so heavy they resist
updrafts and fall through the
clouds as rain.
In Cherrapunji it rains so much
for two reasons:
Elevation: because of the
elevation of Cherrapunji, air
that blows over the plains
below is cooled as it rises to
the higher elevation. This
cooling of the air causes the
moisture trapped in the air
to condense, forming clouds,
which then release rain.
Monsoons: the prevailing
winds in that part of the
world are very heavily laden
with moisture. The constant
supply of moist air for six
months straight results in
almost continual rainfall.
Here's a place that holds a
close second to Cherrapunji:
Mount Waialeale, Kauai
This place holds the
unofficial world record,
because the record is an
estimate
(523.6 in/13.3m)
http://www.extremescience.com/wettest.htm
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