Rainfall refers to the one of water, which evaporates from the land and sea surface and falls again in the form of precipitation. Precipitation is defined as any form of water bodies such as frozen snow, hail, ice, etc., which fall from the sky; while the term ‘rainfall’ means all forms of water bodies condensing from atmospheric water vapour and then falling under gravity along with dust, smoke and other airborne particulate matter.
The rainfall is more over the oceans than on the landmasses of the world because of being great sources of water.
Wherever mountains run parallel to the coast, the rain is greater on the coastal plain, on the windward side and it decreases towards the leeward side.
On the basis of the total amount of annual precipitation, major precipitation regimes of the world are identified as follows.
The equatorial belt, the windward slopes of the mountains along the western coasts in the cool temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm per annum.
Interior continental areas receive moderate rainfall varying from 100 – 200 cm per annum. The coastal areas of the continents receive moderate amount of rainfall. The central parts of the tropical land and the eastern and interior parts of the temperate lands receive rainfall varying between 50 – 100 cm per annum.
Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall-less than 50 cm per annum. Seasonal distribution of rainfall provides an important aspect to judge its effectiveness.
