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 1290
meters above sea level and much of the torrential rains run off the
mountains into the valley below. 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): Lloro,
Colombia |
