South-west monsoon

South-west monsoon [Climate of India]

The origin and formation of the winds:

The south-west monsoon winds originate in the Indian Ocean. The high temperature period during summer gives rise to vast low- pressure areas in the north-eastern regions of India. During this time cool and high- pressure area develops in the Indian Ocean. Thus a system of winds is formed over the Indian Ocean. These winds are termed as south-west monsoon winds. The south-west monsoon winds begin io blow from the month of June and continue to blow till September every year. Kerala, because of its proximity to the Indian Ocean is the first state to get monsoon winds. The moisture laden monsoon winds bring heavy rainfall to Kerala in the first week of June. They travel across the greater part of India during June and September bringing along rainy season in India. The south-west monsoon winds blow in two branches- the Arabian Sea Branch and the Bay of Bengal Branch.

The Arabian Sea Branch:

These winds blow over the Arabian Sea and strike against the Western Ghats. These moisture-laden winds are forced to ascend over the slopes of the Ghats giving along plentiful rainfall to the Western Coastal Plains. The farmers of Kerala, western Karnataka and southern Maharashtra are the beneficiaries of this branch of the south-west monsoon winds.

A section of the Arabian Sea branch moves towards the north and crosses over the Vindhyas and Satpura ranges. These winds strike against the Rajmahal hills and cause heavy to very heavy rains in the Chotanagpur regions. Another section of the Arabian Sea branch travels further north and moves towards Rajasthan. The Aravalli hills that lie parallel to the direction of the winds help it to reach Himachal Pradesh. The Aravalli do not act as climatic barriers, thus preventing Rajasthan to get its share of rainfall.

The Bay of Bengal branch:

The moisture laden Bay of Bengal branch of the south-west monsoon winds, on its way to the north, strikes against the Kasi, Garo and Jaintia Hills. The winds take a sudden rise over the funnel shaped hills and cause very heavy rains to the place called Cherrapunji. Incidentally, Cherrapunji records highest rainfall in India. A section of the winds belonging to the Bay of Bengal branch moves towards the west and gives rains to the Gangetic plains. The winds then move further westwards and cause rainfall to the places such as Punjab and Haryana.

The two branches meet at the Siwaliks:

The Arabian Sea branch and the Bay of Bengal branch of the monsoon winds meet at the foot-hills of the Siwaliks ranges of the Himalayan Mountains. The merged winds give abundant rains along the foothills of the Himalayas. Thus south-west monsoon winds bring rainfall to the greater part of India. During the entire rainy season, southern Andhra Pradesh and Tamil Nadu remain dry. This is mainly because the regions lie on the rain-shadow regions of the south-west monsoon winds.