How does it rain?

We all know that clouds give us rain. Whenever the sky is cloudy, we know that it is going to rain. The formation of raindrops in clouds is a long and complicated process of nature. We can understand this natural process in the following way.

During summer, the water of rivers, lakes and seas is converted into vapour by the heat of the sun. These vapour mixed with the air give hot and humid air. Since water vapours are lighter than air, they go on rising high in the sky and even a slight decrease in the surrounding temperature changes them into clouds. We know that there are dust particles in air. When clouds move from hotter regions to colder ones, water vapours start condensing on these dust particles, forming droplets of rain in the clouds. Only when the size of these droplets increases due to further condensation, they start falling down on the Earth due to the force of gravity, and we say that it is raining.

Thus for rains, it is essential that hot and humid air should be lifted up so that water vapour get condensed. Lifting of air takes place in several ways such as orographic lifting, frontal lifting and convectional lifting. Orographic lifting occurs when air is forced upwards by a natural barrier, like a mountain. In frontal lifting cool air of one air mass pushes beneath the warm air of the other air mass. Convectional lifting occurs due to the heat of the sun. Do you know that the highest rainfall of the world is at Cherapunji (Assam) in India? The average annual rainfall of this place is 1,200 cm. In 1861 the total rainfall recorded here was 2,175 cm.

In colder regions, condensation of water vapour takes place not only on the dust particles, but also on the small particles of ice formed in the clouds. Condensation also takes place on ions produced by lightning in the air. Water condensed on ice particles also falls down on the Earth in the form of rains.