Different places on the earth’s surface receive different amounts of rainfall in a year and that too in different seasons.
General variation in rainfall
In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily.
The coastal areas of the world receive greater amounts of rainfall than the interior of the continents.
The rainfall is more over the oceans than on the landmasses of the world because of being great sources of water.
Between the latitudes 350 and 400 N and S of the equator, the rain is heavier on the eastern coasts and goes on decreasing towards the west.
But, between 450 and 650 N and S of equator, due to the westerlies, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.
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.
In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in the western parts of cool temperate regions.
Seasonal distribution of rainfall provides an important aspect to judge its effectiveness.
Major precipitation regimes of the world
On the basis of the total amount of annual precipitation, major precipitation regimes of the world are identified as follows.
Regions having rainfall of over 200 cm per annum
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.
Regions having rainfall varying from 100 – 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.
Regions having rainfall varying between 50 – 100 cm per annum
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.
Regions having rainfall-less than 50 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.
