Rainfall is the amount of precipitation, in the form of rain (water from clouds), that descends onto the surface of Earth, whether it is on land or water.
Based on the source of uplifting of air, there are three main types of rainfall –
Convectional Rainfall :-
It is a typical of warm moist air by heating from the ground surface. As a result of heating, the air expends and forced to rise to great height. As the air rises, it cools and become saturated and dew point temperature is attained. By further cooling precipitation occurs.
- Necessary conditions for convectional rainfall
- Intense heating of the surface which causes the air to expend and rise.
- Abundant supply of moisture in the air to produce a very high relative humidity.
Turbulence in the atmosphere and surface obstructions like hills can provide initial upward push.
This rainfall occurs throughout the year nearly equator daily in afternoon. In the middle latitudes, convectional rainfall occurs in early summer in continental interior.
Frontal Rainfall :-
This type of precipitation is associated with a cyclonic activity and occurs along the frontal zone of convergence particularly at the ITCZ and at the polar fronts.
In a zone of horizontal convergence, the warm air forced up over the cold air. In such slow ascend, pressure decreases, air expends and cools, condensation and cooling produce a precipitation. These fronts and associated weather phenomenon are best developed in the middle latitudes.
Orographic/ Relief Rainfall :-
It occurs when large mass of air is forced to rise across landforms barriers, such as high mountains, plateau, escarpment or over high hills.
The leeward side is characteristically drier are called rain shadow zone. It’s most common on the windward slopes of the mountain where the on-shore moisture come from sea.
Ideal condition for heavy continuous mountain frontier close to the coast and the winds from off a warm ocean meet the barrier at right angles.
This is exactly case with Western ghats which lies perpendicular to SW monsoon.
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