Annual Rainfall in Sri Lanka

 

Figure: Annual Average Rainfall Map
Source: Department of Meteorology Sri Lanka

There are several  type of Rain fall in Sri Lanka. They are Monsoonal Rain, Convectional Rain, Depressional Rain and Orographic Rain (Relief Rain). 

Monsoon Rainfall

Monsoon is major wind system that seasonally reverse its direction that cause rainfall. Further, Monsoon cause wet seasons and dry seasons also. Most of tropics experience rainy season as a result of  monsoon. The Indian ocean is most frequently connected with monsoons that blow cold to warn region.
 There are four monsoon rainfall seasons in Sri Lanka as fallows
(1) First inter monsoon season ( March to April)
(2) South-west monsoon season ( May to September)
(3) Second inter monsoon season (October to November)
(4) North-East monsoon season (December to February)

Annual average rainfall of Sri Lanka is varies from 900mm in dry zone to 5000mm in wet zone.

Pdf Download of Rainfall Data : Click Here to Download

Convectional Rain


Convectional Rainfall  Source: Google

When Sun shine on the Erath surface a thin layer of air nearby is heated. This heated air rises
upward along with water vapors, because of it is warmer than the surrounding air(warm air rises). it gets colder, when reaches higher altitude in the atmosphere. As a result, water vapors condense into water and create clouds that eventually fall as a rain.    

Orographic Rainfall ( Relief Rain)


Orographic Rainfall  Source: Google

Orographic or Relief Rainfall occurs when warm moist air that has been blowing over surface of water bodies is forced to rise on reaching topographic barriers like mountains. The rising air cools , since the air higher up in the atmosphere is colder. if it has enough moisture, water vapors condense into water form clouds and eventually fall as a rain. Ritigala is the real example in Sri Lanka for orographic rainfall is occurred.   


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