Rain is not only essential for plant growth but it is equally important for better survival of life. Formation of rainfall occurs when saturated air is heated and rises either by a frontal action or by a mountain. With the rising process saturated air or water vapour cools down and further they attach themselves to tiny particles of dust salt, seeds or smoke in the atmosphere. These attached particles are also known as condensed nuclei. When so many condensed nuclei join together then there occurs a process of condensation. This condensation process is necessary for formation of rain drop. Further raindrop leads to the formation of clouds.

On the basis of origin rainfall is classified into three types:

• Conventional rainfall
• Orographic rainfall or relief rainfall
• Cyclonic rainfall or frontal rainfall

Convectional Rainfall:

The formation of convectional rainfall occurs when air is on the surface of the earth or a few metre above the surface of the earth it is heated by the sun. Once the air is heated it becomes lighter and further this lighter air rises up and cools down and condenses on the condensation nuclei which are present in the atmosphere. This is because of the fact that only a small surface of area is covered by converging air. As soon as air converges it gets condense to form a thick cumulus cloud. as the cloud Rises up they become unstable and because of this instability cloud drops on the ground in the form of raindrops or rainfall.

Characteristic Features of Conventional Rainfall:

• Once the air gets heated they become light and rise in a convection current.
• With the rise of air they expand and the temperature drops down and by this condensation process takes place and forms clouds.
• Convectional rainfall is usually in the summer or the hotter part of the day.
• Sach rainfall is mainly associated with hail and graupel.
• The equatorial region and internal part of the continents mainly in the Northern hemisphere receive conventional rainfall.

Orographic or Relief Rainfall:

When wind forces moist air landwards towards the mountain’s terrain then the mountain further lifts the moist air in an upward direction that is into the atmosphere. Once the air reaches the atmosphere it cools down and undergoes a precipitation process.

With rising in winter water vapour they started becoming unstable and heavy and because of this they develop around conventional nuclei and form thick clouds. Further, this cloud moves up and becomes an unstable water droplet. And after this, they fall on the ground as raindrops.

Characteristic Features of Orographic or Relief Rainfall:

• The principal characteristic behind this type of rainfall is that the windward slope gets heavy rainfall.
• The reason located on the leeward side opposite side is known to be rain-shadow area.
• This rainfall is seen in mountainous areas and along hills.
• Mountains act as an obstacle that force vapour to rise which leads to orographic rainfall.

Cyclonic or Frontal Rainfall:

It is the last type of rainfall and occurs when two air masses that have different characteristics combine together. For example when a warm Maritime air mass combines with a cold heavier air mass then in that case the warm air mass is undercut by cold air mass. And because of this warm air mass is forced to move up because of its lightweightness. And warm water vapour cools down as it rises up which leads to the condensation process and a cloud is formed and the condensation nuclei in the atmosphere. With rise in clouds they become unstable as more water droplets are accumulated in the cloud and they fall on the ground in the form of cyclonic rainfall.

Characteristic Features of Cyclonic or Frontal Rainfall:

• The Tropic and Temperate Zones receive such rainfall.
• The layer which separates two masses of air is known as the front.
• The type of rainfall is mainly for a few hours to a few days.