WHY DOES IT RAIN?

There has always been the same amount of water on the earth, but the amount floating around in the air as water vapour or clouds depends on how warm it is. Warmer air holds more water while colder air holds less. This is an important factor when it comes to how heavy a rainfall is. As we all probably remember from school, when water on the Earth is heated by the Sun, it evaporates and turns into water vapour which rises into the air. When the air cools it condenses around some dust or other particles in the air, these are called condensation nuclei. These small droplets then become visible as clouds. Some droplets fall through the cloud and coalesce into raindrops on their way down. As more and more droplets join together they become too heavy and fall from the cloud as rain.