Why Does India Have Monsoons?
The seasonal winds of southwest Asia known as monsoons are associated particularly with India because of the tremendous effects they have on the lives of the inhabitants. The winds are drawn to India by changes in the temperature of the great land mass. The Indian Monsoon turns large parts of India from a kind of semi-desert into green lands.
A good monsoon season with plenty of rain means a comparatively good supply of food. A bad monsoon with little rain means a bad rice crop and, perhaps, starvation for many millions. Monsoon comes from the Arabic mausim, meaning season. The term was first used in English in British India and neighbouring countries to refer to the big seasonal winds blowing from the Bay of Bengal and Arabian Sea in the southwest bringing heavy rainfall to the area. The summer season monsoon is a great inrush of moisture-laden air from the ocean. The winter monsoon blows from the land to the sea.
In India there are
three seasons: the hot dry season from March to June; the hot wet season from
June to November; and the cool dry season from December to March. During the
hot dry season the great plains of northern India becomes like a furnace and a
region of low pressure develops.
By mid-June, the pressure is low all the way to the Equator and draws the south-east trade winds to India, filled with water-vapor as they cross the Indian Ocean. When they meet the hot dry air over India, violent thunderstorms result, followed by steady rain in July. By November India has received three-quarters of its annual rainfall.
Then the land mass cools and the lower pressure to the south attracts the north east trade winds. These bring no rain to India except to the Coromandel Coast and Sri Lanka (formerly Ceylon), where the rainfall in late September is heavy, because the winds have picked up water vapor as they cross the Bay of Bengal.