Indian Monsoon – FREE UPSC Notes/PDF

The Monsoon is a lengthy and interesting topic but not so difficult. It only seems difficult when you are not aware of the basic concepts of geography as this is somewhat a technical subject. But try not to fear, just keep practising and let me help you understand the concepts.

The basic definition of Monsoon is ‘ the seasonal reversal of winds in the tropical area’.

Now let’s understand each word of the above definition. The seasonal reversal of winds mean that the winds move from sea to Indian subcontinent in south-west direction (in summer) and then, after some months ( in winter) it reverses from land to sea again in north-east direction. It happens in tropical areas only between 20° N to 20° S. This was in short, what happens in monsoon. Now, we will see, why does it happen.

Source: EDEN IAS

The winds move from High Pressure to Low Pressure area. High Pressure area is created when winds subside (when winds come from the sky to the land). Low Pressure area is created when winds converge (when winds go from the land to the sky and create clouds). There are so many reasons behind this. We will understand it later. Just remember the first line.

The reasons are: 

(a) In the summer season, the landmass of India is very much heated and low pressure develops here as compare to the sea. So, the sea has relatively high pressure. Therefore, the winds blow from sea to land. (Differential Heating and cooling of land and water)

(b) An Inter Tropical Convergence Zone (ITCZ) is a low pressure belt that moves from north to south time to time. It is created because of the perpendicular hot rays of the sun. In the summer season, the ITCZ shifts to the northern Indian subcontinent over Ganga Plains. This again develops a low pressure area and intensifies the wind blowing from sea to land. (Shift in the position of ITCZ)

(c) In summer, the Tibetan plateau gets intensely heated and creates a low pressure area. It again intensifies the wind blowing from sea to land. (Tibetan plateau gets intensely heated)

(d) At about 20°S over the Indian Ocean, a high-pressure area is developed east of Madagascar ( near the Mascarene Islands). This also intensifies the wind blow from sea to land. Because winds blow from high pressure to low pressure area. (High-pressure area, east of Madagascar)

Now we’ll discuss it in detail in the technical language according to UPSC exam point of view.

The Indian Monsoon has two phases (i) Advancing Monsoon and (ii) Retreating Monsoon.

Advancing Monsoon

Source: NCERT
  • By early June, the northern plains intensify and a low-pressure area is developed in the northern part of the Indian subcontinent. It attracts the south-east trade winds and crosses the equator and blows in south-westerly direction entering the Indian peninsula as the south-west monsoon.
  • These winds then cut off in two branches viz. Arabian sea branch and Bay of Bengal branch. The Arabian sea branch leads to rainfall in the western part of the country, Deccan plateau and even in some parts of Madhya Pradesh. On the other hand, Bay of Bengal branch leads to rainfall in the northeastern part of the country and then blow from east to west leading to rainfall in western Uttar Pradesh, Punjab, Haryana and east Rajasthan. (so it is Bay of Bengal branch which brings rainfall to Rajasthan, U.P, Punjab, Haryana and Delhi. It is a point to be remembered)
  • Since there is a range of mountains in western ghats, the monsoon enters only through the gaps between the mountain ranges. Therefore, some parts experience droughts and some parts experience heavy rainfall in western India.
  • Talking about Bay of Bengal branch, it leads to less rainfall in the east coast of India during advancing monsoon, because it blows parallel to the coast and cannot bring the moisture from the sea to land. It leads to heavy rainfall in the northeastern part of the country. Mawsynram in the southern ranges of the Khasi Hills (Meghalaya) receives the highest average rainfall in the world.
  • Because of the syntaxial bend of Himalayas in the north-eastern part of the country, the monsoon gets diverted to the western part of the country moving parallel to the Himalayas. Rainfall in the Ganga valley decreases from the east to the west. Rajasthan and parts of Gujarat get scanty rainfall.

Retreating Monsoon

Source: NCERT
  • During October-November, the sun moves towards the south, this leads to weakening of low-pressure belt in the northern part of the Indian subcontinent and it gradually replaces by a high-pressure system.
  • The south-west monsoon winds weaken and start withdrawing gradually by the beginning of October. This is called North-east monsoon.
  • One point to be remembered is that the east coast of India gets heavy rainfall during this time and Chennai sometimes experience flood-like conditions.
  • When the sun moves southward in October-November, the Bay of Bengal gets intensely heated and cyclones develop here (as it fulfils all the criteria to form cyclones). It causes severe damage to Kaveri-Godavari region, Odisha and West Bengal.
  • The Andaman and Nicobar islands of India, receive rainfall throughout the year.

Now, I think you can remember the definition of Monsoon.