Early Onset of Indian Monsoon

Syllabus: GSI/ Indian Physical Geography

In Context

• As per the IMD, there are chances of early onset of the southwest monsoon. The normal onset date of the monsoon over Kerala is June 1 and it usually takes about 10 days for the system to reach Kerala from the Nicobar islands.

Mechanism of the Indian Monsoon: The Driving Forces

• Differential Heating of Land and Sea: In summer, India’s landmass heats faster than the ocean, creating low pressure over land and drawing in moisture-laden winds from the sea.
• Inter-Tropical Convergence Zone (ITCZ): The ITCZ, where trade winds meet near the equator, shifts north during summer, intensifying low pressure over the Indo-Gangetic plain and drawing in monsoon winds.
• Tibetan Plateau: Its high elevation heats up, creating an upper-air low-pressure zone that strengthens vertical circulation and attracts monsoon winds.
• Tropical Easterly Jet: Develops during summer, strengthening monsoon trough and rainfall.
• ENSO:
  • El Niño: Warms Pacific waters, usually weakening Indian monsoon.
  • La Niña: Cools Pacific, often strengthening monsoon.
• Indian Ocean Dipole (IOD):
  • Positive IOD: Strengthens monsoon with warm western Indian Ocean.
  • Negative IOD: Weakens monsoon.

Onset and Advancement

• Arabian Sea Branch: Hits Kerala around June 1, moves up the west coast, bringing heavy rain to Western Ghats and inland states.
• Bay of Bengal Branch: Reaches Northeast India in early June, then moves westward along the Indo-Gangetic plain. India is usually fully covered by mid-July.
• Retreat of the Monsoon: Retreat begins in October from northwest India. Clear skies and residual moisture cause hot, humid conditions called “October heat.”
• Reversal of wind direction brings rain to the southeastern coast, notably Tamil Nadu and Andhra Pradesh.

Impact of the Monsoon

• Agriculture: Essential for Kharif crops like rice and maize. A good monsoon improves yields; a poor one leads to drought.
• Economy: Monsoon-linked agriculture influences GDP, rural income, and food prices.
• Water Resources and Hydropower: Rains recharge rivers and reservoirs, crucial for drinking water, irrigation, and electricity.
• Environment and Culture: Supports biodiversity and cultural traditions like festivals celebrating rain.
• Disasters: Heavy rains can trigger floods, landslides, and other disasters, especially in vulnerable regions.

Recent Government Initiatives to Improve Monsoon Forecasting

• Monsoon Mission: Launched in 2012 by the Ministry of Earth Sciences it was a major initiative aimed at enhancing the accuracy of monsoon forecasting.
• National Supercomputing Mission: Aimed at enhancing computational infrastructure needed for running high-end dynamical weather models.
• ICAR & IMD Collab: The IMD, in collaboration with the Indian Council of Agricultural Research (ICAR), provides Agromet Advisory Services.

Source: TH