Types of Rainfall

Introduction to Rain and its types

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapour. Rain is an important factor in the water cycle. It handles most of the freshwater deposited on earth. Rain provides conditions for many ecosystems to co-exist in a habitat. It powers our hydroelectric plants. It is also used in crop irrigation.

There are three rainfall types:

1. Convectional rainfall
2. Orographic or relief rainfall
3. Cyclonic or frontal rainfall

Convectional rainfall

Convectional rainfall forms convection currents. It occurs when the earth’s surface becomes more heated than its surroundings. Convectional rainfall happens in an unstable or moist atmosphere. As the temperature gets high, the warmer air rises up. This is called evaporation. As it reaches a certain height, the air cools down and expands. Thus, clouds are formed. The clouds formed are called cumulus clouds. This rainfall type falls with changing intensity in its initial stages.

There are 4 stages in convectional rainfall

1. The heat of the sun makes the surface of the earth hot. Due to this, the warm air rises up.
2. As the warm air rises, it starts to cool down. The water vapour then condenses to form clouds.
3. There is a certain condensation point to be reached. Here clouds are formed.
4. Heavy rainfall starts which include lightning and thunderstorms. Lightning occurs due to an electrical charge between the clouds. 

Convectional rainfall-type occurs in equatorial regions. Rainfall is heavy and there can be some lightning or thunder. Convectional rainfall does not last long. This rainfall type occurs in the summer or during the warmer part of the day. This is the most common rainfall type experienced in the world. Convectional rainfall can also be seen in some parts of the northern hemisphere. 

Convectional rainfall can be termed convective rain. It is a form of light precipitation. This type of rainfall results in convective clouds for example cumulus congestus or cumulonimbus.

Orographic or relief rainfall

Relief rainfall occurs when moist air is lifted near a mountain range. The moist air goes over the mountain range. As it moves further, the air cools down. Due to this orographic clouds are formed which are the source of the rainfall. This rainfall-type falls with the wind on the other side of the mountain range. Some amount of rainfall is on a short distance of the ridge called a spillover. Relief rainfall occurs in mountainous areas

There are 4 stages in convectional rainfall

1. The warm air rises up due to the height of the mountains
2. It rises to a certain level and cools down. Due to this, the clouds form
3. The dry air descends
4. As warm air descends, there is little rainfall on one side of the mountain. 

There are two factors responsible for this rainfall-type

1. Humid atmospheric conditions
2. The inclination of the mountain

Due to the one-sided rainfall, relief rainfall causes floods and hurricanes. This rainfall-type is uncontrollable as it falls rapidly. The side where the wind goes experiences heavy rainfall. The other side is often dry.

The term ‘rain shadow’ area is associated with relief rainfall. As heavy rainfall occurs on only one side of the mountain, the other side experiences low rain. This area that has low rainfall is called the rain shadow area. As a result, the area in the rain shadow is dry. The relief rainfall removes all the moisture from the rainshadow area.

Cyclonic or frontal rainfall

Frontal rainfall-type occurs due to cyclonic activity. A cyclone is a large air mass that rotates along a strong centre of atmospheric pressure. It moves clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. Cyclonic rainfall is also called frontal rainfall because it occurs along the fronts of a cyclone. Frontal rainfall occurs when warm air and cool air meet each other. Warm air is lighter than cool air. So, the warm air rises above the cool air. The air rises to a point where it saturates and heavy rainfall occurs.

There are 4 stages in convectional rainfall

1. Warm air meets cool air.
2. Warm air rises above the cool air.
3. Warm air is cooled and it condenses.
4. Clouds start forming, and rainfall occurs.

The effect of cyclones causes heavy rain, large storms, strong wind, landfalls and tornadoes. Frontal rainfall can cause mass destruction due to its nature. It also causes mass soil erosion. Frontal rainfall occurs in the coastal parts.

Conclusion

In conclusion, we may say that rain is essential for maintaining the balance of the water cycle and the ecosystem on earth. The three types of rainfall types occur due to different reasons and through different phases. It is important to learn them in detail to understand their significance.