Various parts of Tamil Nadu witnessed heavy rains on Wednesday evening. With the formation of a depression over the Bay of Bengal, it is expected that the state will see more rainfall for at least the next two days.

Unlike the rest of India, Tamil Nadu receives it’s rainfall majorly from the North-East Monsoon(Winter Monsoon) and not the South-West Monsoon(Summer Monsoon)

Why?

The Eastern Ghats are lower in altitude than the Western ghats. Due to this the monsoon rains lose its moisture on the western slopes of the Western Ghats and the rest of the plateau and the eastern ghats gets scanty rainfall. As a result Tamil Nadu (Chennai) gets less rain fall during the South West Monsoons.

Two Monsoons of India

• The south-west monsoon (summer monsoon) blows from sea to land after crossing the Indian Ocean, Arabian Sea, and the Bay of Bengal.
  • It brings most of the rainfall in the country, approximately 75% of India’s annual rainfall.
  • It gets its name from the direction in which it travels, from the southwest to the northeast.
• The northeast monsoon (winter monsoon) blows from land to sea.
  • During this period, rainfall is experienced over southern states, mainly Tamil Nadu, Kerala, Andhra Pradesh along with some parts of Telangana and Karnataka.
  • In areas around Jammu and Kashmir, Himachal Pradesh, Uttarakhand and along the northeast, precipitation during this period reported is either in the form of rainfall or snowfall.

What is the northeast (winter) monsoon?

• Though much less heard of, especially in the north of the country, the northeast monsoon is as permanent a feature of the Indian subcontinent’s climate system as the summer monsoon.
• The India Meteorological Department (IMD) recognises October to December as the time for the northeast monsoon.
• During this period, rainfall is experienced over Tamil Nadu, Kerala, and Andhra Pradesh, along with some parts of Telangana and Karnataka.

Difference between Northeast and Southwest monsoons?

• The Northeast monsoon derives its name from the direction in which it travels — from the northeast to the southwest.
• Similarly, the summer monsoon moves in exactly the opposite direction — from the southwest to the northeast. That is why it is called the southwest monsoon.

Where does it rain during the northeast monsoon season?

• The northeast monsoon brings rain to just five of the 36 meteorological divisions in the country — Tamil Nadu (which includes Puducherry), Kerala, Coastal Andhra Pradesh, Rayalaseema and South Interior Karnataka.
• As such, this season contributes only 11 per cent to India’s annual rainfall of 1,187 mm, compared to about 75 per cent in the summer monsoon season (the remaining rain comes in other non-monsoon months).

Impact on northern states:

• Many other parts of the country, like the Gangetic plains and northern states, also receive some rain in November and December but this is not due to the northeast monsoon.
• It is caused mainly by the Western Disturbances, an eastward-moving rain-bearing wind system that originates beyond Afghanistan and Iran, picking up moisture from as far as the Mediterranean Sea, even the Atlantic Ocean.
• In the higher reaches of Jammu and Kashmir, Himachal Pradesh, and Uttarakhand, the precipitation is often in the form of snow.