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Record Rainfall: Cherrapunji, India
A Land of Contrasts
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): Lloro, Colombia