Rainfall Types, Convectional, Orographic, Frontal, Map, Distribution

Rainfall

Rain is a type of precipitation, which means it is water falling from the sky to the ground. Rain is liquid, but there are other types of precipitation too.  Precipitation comes in three forms: liquid, freezing and frozen. Precipitation falls on the earth in various forms. The form depends on the method of formation and the temperature during formation.

Rain is a important part of the water cycle and brings most of the fresh water to Earth. It creates the right conditions for many ecosystems to thrive. Rain also helps generate electricity in hydroelectric plants and is used for watering crops.

There are three types of rainfall:

• Convectional rainfall: This occurs when warm air rises and cools, causing rain.
• Orographic (or relief) rainfall: This happens when moist air rises over mountains, cools, and produces rain.
• Cyclonic (or frontal) rainfall: This occurs when warm and cold air meet, leading to rain.

The article below discusses the various Types of Rainfall based on their origin which is beneficial for UPSC aspirants.

Read More: Evaporation and Condensation

Rainfall Necessary Conditions

There are some necessary conditions required for Rainfall formation such as:

• There should be a sufficient amount of evaporation from the water bodies.
• There should be a wind to carry the water vapour from one place to another
• There should be some way of decreasing the temperature of the moist air.
• Rainfall occurs when the cloud droplets change to raindrops.

Types of Rainfall

Rainfall is classified as Convectional, Orographic, and Convergence rainfall based on the mode of occurrence:

1. Convectional Rainfall

Different surfaces heat up at different rates, causing air near the ground to warm up more than the surrounding air. This warm air is lighter so it rises. As it rises and cools below the dew point, condensation occurs, forming clouds that can lead to thunder and heavy rain. This process is known as convectional rainfall, which is common in equatorial regions and the interior of continents, especially in the northern hemisphere.

Read More: Structure of the Atmosphere

2. Orographic Rainfall

Orographic rainfall occurs when warm air rises over a mountain. As the air goes up, it cools and forms clouds, which then cause rain on the side of the mountain facing the wind. When the air goes down the other side, it warms up and does not bring much rain, creating a dry area called a rainshadow. This kind of rainfall can be seen in places like Cherrapunji in Meghalaya, India.

3. Frontal Rainfall or Cyclonic Rainfall

This happens when big air masses come together. A front forms when a cold polar air mass meets a warm westerly air mass. The warm air rises, and the cold air sinks. These fronts usually occur in temperate areas where cold and warm winds meet. The warm air above the cold air cools down, leading to condensation around tiny particles in the air.

Warm air rises along the slanted front instead of going straight up like in convection. This front is where high pressure, cooling, clouds, and rain happen, and it is called frontogenesis. Frontal rain usually happens in the middle latitudes, where warm westerly winds meet cold polar winds. Frontogenesis is also how temperate cyclones form. In India, these cyclones bring rain during winter, called western disturbances.

Read More: Types of Winds

Rainfall Global Distribution

Rainfall is not uniformly distributed on earth. Different regions of the world receive different amounts of rainfall depending upon their location and seasons. The world can be divided into the following areas based on the rainfall received.

1. Areas of Heavy Rainfall

These regions receive more than 200 cm of annual precipitation. The main areas include the equatorial belt, the mountain slopes of the western coasts in the cool temperate zone and the coastal areas of monsoon lands.

2. Areas of Moderate Rainfall

The regions receive 100 cm to 200 cm of annual precipitation. The main areas lie near the regions of heavy rainfall. The coastal areas in the warm temperate zone also receive moderate precipitation.

3. Areas of Low Rainfall

These regions receive 50 cm to 100 cm of annual precipitation. The main areas lie in the central part of the tropical lands, in the eastern and the interior parts of the temperate lands.

4. Areas of Scanty Rainfall

These regions receive less than 50 cm of annual precipitation. The main areas are the leeward slopes of the mountain ranges, the continental interiors, the western margins of the continents in the tropical areas and the arid deserts.

Read More: Heat Waves

Rainfall Precipitation Seasonal Distribution

The conditions for rain do not happen the same way all year. That’s why rainfall changes with the seasons. Most places in the world get a lot of rain in the summer. Here are the main features of seasonal rainfall:

The equatorial region experiences heavy rainfall all year.

• A few degrees north or south of the equator have wet summers and dry winters.
• The monsoon circulation brings more seasonal contrasts resulting in wet summers as the wind blows onshore and dry winters as the wind blows offshore.
• Seasonal variation, due to the monsoons, is well-developed in the Indian Subcontinent and in Southeast Asia.
• Most of the western coastal areas in the mid-latitudes have dry summers and wet winters due to the presence of the subtropical high-Pressure Belts.
• In the temperate region, the precipitation is cyclonic in nature and cyclones are more common in the winter season. Thus heavy rainfall occurs in winter and not in summer.

Read More: Types of Rocks

Rainfall UPSC

Rainfall is the gravitational fall of atmospheric moisture in the form of water. Snow is the precipitation of white opaque crystals that occurs when the temperature falls below zero degrees Celsius. Rain does not fall unless the cloud droplets become so large as a result of coalescence that the air can no longer hold them. This article discusses the various types of rainfall based on their origin which is beneficial for UPSC aspirants.

Other Indian Geography Topics

Other Fundamental Geography Topics

Sharing is caring!