As we know there are some countries where it rains all time and this continuous rain helps in proper growth of grass and crops. In this unit we will discuss types of rainfall NCERT Notes for UPSC aspirants for Geography syllabus. 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.

Types of Rainfall UPSC (Geography) NCERT Notes: Download PDF Here

Classification of Rainfall

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.

If you are reading the NCERT Notes on Types of Rainfall article, you may also be interested in learning more about the Structure of the atmosphere NCERT Notes

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.

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Effects of Rainfall

Water is considered as one of the most valuable resources on the earth and rainfall is the only way by which all the water reservoirs can be filled. This reservoir’s supply of drinking water is done. Along with that water is also a Habitat for fish to leave, also nourishes the soil for proper vegetation as while doing agriculture practice water helps both people and animals for harvesting and for the consumption process also. Among all the sources of water, rainfall is considered as one of the major sources.

Sometimes rainfall also has a negative effect like it causes soil erosion when rain is having high pH. Along with that, it can also cause natural disasters which destroy properties and lives also.

You can also check the NCERT Notes on Factors Controlling Temperature Distribution here.

Types of Rainfall Based on Humidity

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

1. Light rainfall: In this rainfall rate varies between 0 to 2.5 millimetres.
2. Moderate rainfall: In this rainfall rate varies between 2.6 millimetres 27.6 millimetres.
3. Heavy rainfall: In this rainfall rate is beyond 7.6 millimetres.

Water Cycle or Hydrologic Cycle

When water moves from the river and lakes then in that case they form clouds. All this process is called the water cycle or hydrological cycle. As in this cycle there occurs movement of water from sea to sky and sky to river. So it is impossible to survive without a water cycle or hydrologic cycle. Steps involved in water cycle or hydrologic cycle:

• The cycle begins at sea when water is heated by the rays of the sun as this causes evaporation of seawater. Show sea water turns to water vapour and then to steam. Further, there is rise in water vapour as they are light weighted.
• With increasing, height water vapour gets cooled down and this cooling leads to the condensation of water vapour into water droplets.
• Station of water vapour leads to formation of Clouds. Clouds keep on storing water vapour till they become too heavy and they cannot store anymore.
• Once the cloud gets saturated the precipitation process starts. Further based on temperature precipitation can be of many forms like rain. hailstones, sleet or snow.
• Further this rainfall flows into the river and streams and this river and stream bring back water into the sea and again the water cycle gets started.

You may also be interested to know about NCERT Notes on Highest Peaks In States Of India.

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