When condensed water vapour falls from the atmosphere to the earth’s surface, it is called precipitation. Rain and snow rain the common forms of precipitation.
When air-temperature falls more and more condensation of water vapour takes place. As a result, the tiny droplets of water suspended in the upper air get lager. A stage is reached when they become too heavy for the air to support. Consequently, these begin to fall towards the earth’s surface. On the way down, more of the small droplets are picked up by the larger falling ones so that they grow further in size and weight. The result is rain.
Excessive cooling of the air may cause ice crystals or snow flakes to from instead of drops of water, causing a snowfall.
Sometimes, sudden and strong currents of air force rain drops into the very cold upper air, causing them to freeze. Small balls of ice are thus formed. They may grow further in size before falling down to the surface as hail. Hailstones are very damaging. They ruin crops and can even kill animals caught in a hail- storm.
Types of Rainfall 
Rainfall can be caused in several ways. There major types of rainfall according to their mode of co-currence.
Relief rain
Sometimes mature laden winds, coming from one direction, blow against a mountain barrier. The air is then forced to rise so that it cools. The result is that a greater part of its water vapour condenses and falls as rain. This kind of rain is called relief rain or orographic rain.
The side of the mountain that faces the wind is known as the windward side and the opposite side of the mountain is called the leeward said. And light on the leeward side. Land on the leeward side of a mountain over which little rain or no rain falls is known as the rain shadow area.
A good example of such rainfall is found peninsular India. The south-west monsoons in summer cause very heavy rainfall on the Konkani coast and the western sloes of the Western Ghats, whereas the leeward side on the plateau receives very little rainfall.
Convectional Rain
When, is land heated by the sun, the air close to it beings to expand and become lighter. The light air moves upwards in a convectional correct. The air cools on reaching a great height and if it is most, the water vapour in it condenses causing rainfall. This is known as convectional rain.
The convectional type of rainfall is usually torrential and accompanied by thunder and lightning. This type of rainfall is common in the equatorial regions
Cyclonic Rain
This type of rainfall occurs in depression or cyclones which are areas of low air pressure. Basically it is due to the meeting of warm and cold air masses. The mass of warm air will be gradually lifted up above the cold air mass. When the warm air is forced to rise, cooling and condensation take place. This may result. This type of rainfall is called cyclonic rain.
Measuring Rainfall
Some places get more rain than others. Even the same place does not always get the same amount of rain from year. We need to measure it. You have already learnt how to do it with a rain-gauge.