Uneven Distribution Of Precipitation
Earth's average annual rainfall is about 1,000 mm, corresponding to 50,000 billion tonnes of rain, snow, sleet, and hail. Most rain falls in the tropics, particularly where mountains force wet ocean winds to high altitudes such as in north-western South America and the Bay of Bengal. The air is cooled with altitude and sheds its water vapour as rain. Interior continental regions are far away from the wet ocean winds and often receive so little precipitation that evaporation exceeds precipitation.
The tropics are often struck by heavy rain, particularly in regions with high mountains.