From UPSC perspective, the following things are important :
Prelims level : Retreat of Monsoon
Mains level : Not Much
The southwest monsoon rainfall, 7% more than normal, has started to withdraw.
What is Monsoon Withdrawal/Retreat?
- In India, retreating monsoon is the withdrawal of south-west monsoon winds from North India.
- The withdrawal is gradual and takes about three months.
- With the retreat of the monsoons, the clouds disappear and the sky becomes clear. The day temperature starts falling steeply.
- Monsoon rains weaken all over India except few southeastern states.
- It is helpful in Rabi crop cultivation.
Factors affecting the retreat
Two predominant factors cause the phenomenon:
(1) Land topography
- First, the low mountain range in each region runs from north to south, shielding it from west-bound winds that trigger summer monsoon.
- After summer, the range aids in the ‘orographic lift’ or rising of east-bound air mass from a lower to higher elevation, forming clouds and resulting in rain.
(2) Atmospheric convection
- The second factor is atmospheric convection or vertical movement of air.
- As the earth is heated by the sun, different surfaces absorb different amounts of energy and convection may occur where the surface heats up very rapidly.
- As the surface warms, it heats the overlying air, which gradually becomes less dense than the surrounding air and begins to rise.
- This condition is more favorable from September to February because of the role played by sea surface temperature or water temperature.
Immediate factors influencing withdrawal
- The withdrawal of the monsoon is based on meteorological conditions such as-
- Anti-cyclonic circulation (dry air that is the opposite of a cyclone)
- Absence of rain in the past five days and
- Dry weather conditions over the region
When does it occur?
- The monsoon withdrawal is a long-drawn process and extends into mid-October, though the IMD considers September 30 to be the final day of the season over India.
- The rain after that is categorised as “post-monsoon” rainfall.
Try this PYQ:
Q.The seasonal reversal of winds is the typical characteristic of:
(a) Equatorial climate
(b) Mediterranean climate
(c) Monsoon climate
(d) All of the above climates
Post your answers here.