What is Rain? How it occurs? Types of Rainfall & More

Rain is something we’ve all encountered ever since we were kids. Sometimes we have fun in the rain -playing about, sometimes we need the water for drinking, domestic and agricultural purposes whereas other times we don’t want rainfall to disrupt our activities. Human life and lifestyle depend on rain immensely as it affects everything around us. Rain is vital for the life of all beings on the planet. However, excess rainfall may also claim lives by causing floods and landslides. 

So, What is Rain?

Rain is nothing but precipitation accumulated or liquid water condensed as droplets due to the atmospheric conditions from water vapor becoming heavy enough to fall by the effect of gravity.

Rain is the most important aspect of the water cycle and is the driving force behind the deposition of freshwater on Earth. Rain provides necessary conditions for many ecosystems, power plants, and irrigation systems to function. 

Rainfall occurs due to the movement of moisture along with three-dimensional temperature and moisture zones and contrasts, which are referred to as weather fronts. If the required moisture and upward motion are present, rainfall occurs from convective clouds or clouds with upward vertical movement. 

The urban heat island effect and global warming have been found to cause changes in precipitation levels and patterns around the globe. Rain is also thought to occur on other planets where precipitation of methane, neon, sulfuric acid, or iron occurs in place of water. 

When Does it Rain?

Rainfall occurs when the cloud droplets grow big and heavy enough to fall out of clouds in the form of raindrops by its own weight. Rainfall is usually seen during the winter season, and the rainfall in summer is due to the melting of snowflakes as they pass through warm air between the clouds and the ground. 

How to Measure Precipitation Values? 

Rainfall can be calculated by observing the depth of the water level on the surface, with the exception of the amount of water absorbed by the groundwater levels. Accurate measurement of this depth is a bit tricky.

Rainfall levels are measured by the aid of a rain gauge tool, which is essentially a cylindrical container with a flat base that funnels rainwater into a narrow inner container to read magnified water measurements.

Snowfall can be measured by using a ruler to scale the depth right after it stops snowing. It’s a bit difficult as the wind moves snow from one location to another, but it can be achieved. A level ground distant from buildings and trees is ideal for recording precipitation measurements. 

Why rain is Important?

The amount of rainfall varies from location to location and from time to time. Some places like Ireland have frequent rainfall, which helps in growing and farming crops and other plants. Rain is one of the essential factors needed for life and the main source of freshwater on the planet, making it impossible to survive without rain. The life of all creatures on Earth thus depends on rain for survival. 

What is the Rainwater Cycle?

Water from rivers, streams, oceans, and other water sources moves up to the sky to participate in cloud formation during important parts of the water or hydrological cycle. This cycle is responsible for the distribution and redistribution of water around the planet, moving water from the sea to sky, the sky to the river, and likewise. Without the rainwater cycle, no streams, lakes, rivers, ponds, or even oceans would exist. Thus this cycle is vital for the survival of all living beings on the Earth. 

Let’s look into some stages of the rainwater cycle:

1

Stage 1 - Evaporation

The water warms up in the sea and oceans by the heat of the sun, leading to evaporation of seawater, which kicks off the initiation of this cycle. Water vapor tends to be light when it rises above as hot air and further turns into steam.

2

Stage 2 - Condenstation 

Water vapor cools down as it rises due to the increase in height. This cooling leads to condensation of the vapor as it can not store water droplets when it is cooled.

3

Stage 3 - Formation of Clouds 

Clouds are formed when the vapor is completely condensed, and the cloud cannot store any more vapor. Precipitation begins after the cloud attains saturation.

4

Step 4 - Precipitation

Precipitation may occur in different forms like rain, snow, sleet or hailstones depending upon the location, temperature, and other atmospheric conditions

5

Stage 5 - Rainfall

This rainfall or precipitation flows back into rivers and streams, which lead to the oceans so that the cycle can start afresh. 

Diagramatic Representation of Rainwater Cycle

What are the Different Types of Rainfall

Rainfall is classified into different categories based on a variety of factors, including the response of the source for uplifting or causing the rise of warm air. Let’s look into the three types of rainfall

Relief/Orographic Rainfall 

This kind of rainfall is usually observed in areas with mountains or seas, frequently seen in mountains beside the sea. 

orographic rainfall

Here, heavy moisture wind rises upwards after the wind comes into contact with a mountain post origin from the sea. After the wind attains a certain height, it is cooled to form clouds.

The cloud saturated with water vapor deposits precipitation on the mountain's front side facing the sea called windward side. Most precipitation occurs on the windward side before it meets the other side called the leeward side, where it rains in minute levels as such leeward sides experience very little rainfall leasing to moist and rich climate on the windward slope and dry, sheltered climate at the leeward side.

Such relief rainfall is observed in Hawaii, Sierra Nevada, and the Andes.

Convectional Rainfall

Convectional rainfall is that rainfall which occurs all of a sudden, leading to the transformation of a bright, sunny day to a dark, cloudy day with a thundering atmosphere.

convectional rainfall

This usually happens on hot days, causing thundery showers due to cumulus clouds. Cumulus clouds are formed when the sun heats up the ground, leading to the surrounding air became warm and hot, causing it to move upwards to cool down and form clouds on condensation. 

Saturation of such clouds causes precipitation and heavy, thundery showers on a hot day as the hot sun warms the air. 

Frontal/Cyclonic Rainfall

Frontal/Cyclonic Rainfall occurs due to the contact of warm and tropical air masses with cold, polar air masses.

frontal rainfall

The air in the warm front rises over the cold front so that the air is cooled and condensed to form a stratus cloud whose saturation leads to precipitation. This kind of rainfall is frequent in Britain and Ireland.

Things to Know About the Different Types of Rainfall:

Relief/Orographic Rainfall 

  • This occurs when large air masses rise across landform barriers like high mountain ranges, plateaus, etc.
  • The leeward side of the mountain is a barrier where ascending air and it’s warming is less, this called rain shadow region.
  • Moisture-laden winds that hit the windward slopes originate from the sea.
  • High relatively continuous mountain frontier close to the coast and winds from a warm ocean meeting the barrier at the right angles is necessary for such rainfall.
  • This is observed in the Western Ghats of India during the south-west monsoon season.

Convectional Rainfall

  • Generally observed when warm moist air on ground surfaces is heated, leading to the expansion of air, causing it to rise to great heights.
  • Rising of warm air cools it down, and the dew point temperature is attained when clouds are formed, leading to precipitation. 
  • Turbulence and surface obstructions such as hills and mountains, provide the initial upward push for air to rise. 
  • This kind of rainfall occurs throughout the year near the equator, and early summer at other latitudes. 
  • Necessary conditions for Convective rainfall:
  • Intense heating which causes air on the surface to expand and rise.
  • Abundant moisture supply to ensure high relative humidity.

Frontal/Cyclonic Rainfall

  • Such precipitation activity is associated with the cyclonic activity.
  • It occurs along the frontal zone.
  • It is a slow ascend where the pressure decreases, air expands, and cools, leading to precipitation from condensed and saturated clouds.
  • They are best developed in the middle latitudes.
  • Most winter rainfall in low lands is cyclonic or frontal in origin. 

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