Western Disturbances

In News 

• Western disturbances bring rainfall to north and central parts of India.

What is Western Disturbance (WD)?

• It is an extra-tropical storm that originates in the Mediterranean region.
  • The disturbance travels from the “western” to the eastern direction and  gradually travels across the middle-east from Iran, Afghanistan and Pakistan to enter the Indian subcontinent.
    • Disturbance means an area of “disturbed” or reduced air pressure. 
      • Equilibrium exists in nature due to which the air in a region tries to normalize its pressure.
  • In the term “extra-tropical storm”, the storm refers to low pressure. 
    • “Extra-tropical” means outside the tropics (as WD originates outside the tropical region). 

Image Courtesy: Weatherview

Impacts 

• It brings rainfall, snowfall, and fog to northern India.
• WD is important for the agriculture of the Rabi crop in the Northern subcontinent.
• The WD is not always the harbinger of good weather and Sometimes, they can cause extreme weather events like floods, flash floods, landslides, dust storms, hail storms and cold waves killing people, destroying infrastructure and impacting livelihoods.
• WD brings winter and pre-monsoon rain and is important for the development of the Rabi crop in the Northern subcontinent.

Additional Information 

Monsoon

• It is a seasonal change in the direction of the prevailing or strongest winds of a region.
• It always blows from cold to warm regions and causes wet and dry seasons throughout much of the tropics.
• Monsoons are most often associated with the Indian Ocean.
  • The summer monsoon and the winter monsoon determine the climate for most of India and Southeast Asia.
• Summer Monsoon
  • It is also called southwest monsoon, which derives its name from winds that blow from a south-westerly direction in the Indian subcontinent.
  • It reaches India from June to September and significantly decides the state of agricultural productivity in India, which in turn, decides the state of the economy.
  • Major factors responsible for the onset of summer monsoon in India are Mascarene High, Coriolis Force, Indian summer, El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD).
    • Compared to the roles of Mascarene High, Coriolis Force, India’s summer season and ENSO, IOD’s role has been discovered recently.
    • However, the relation between IOD and monsoon rainfall is still being debated and has not been fully comprehended.
  • Significance
    • India and Southeast Asia depend on the summer monsoon as agriculture relies on the yearly rain.
    • Many areas in these countries do not have large irrigation systems surrounding lakes, rivers, or snowmelt areas so the summer monsoon fills wells and aquifers for the rest of the year.
    • Dairy farms, which help make India the largest milk producer in the world, also depend on the monsoon rains to keep cows healthy and well-fed.
    • Industry in India and Southeast Asia also relies on it as a great deal of electricity in the region is produced by hydroelectric power plants.
• Winter Monsoon
  • The Indian Oceans winter monsoon, which lasts from October to April, is less well-known than its rainy summer equivalent.
  • The dry winter monsoon blows from the northeast and winds start in the air above Mongolia and northwestern China.
  • Winter monsoons are less powerful than summer monsoons in Southeast Asia, in part because the Himalaya Mountains prevent much of the wind and moisture of the monsoons from reaching the coast.
  • These are sometimes associated with droughts, however, not all winter monsoons are dry.
  • Unlike the western part of Southeast Asia, the eastern, Pacific coast of Southeast Asia experiences its rainy season in the winter.
    • The winter monsoon brings moist air from the South China Sea to areas like Indonesia and Malaysia.

(Image Courtesy: Britannica)

Source: FP