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What are Western Disturbances? UPSC Notes

Western Disturbances are weather systems (specifically extra-tropical cyclones) that bring rain, snowfall, and cloudy weather to north-western India,
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🌧️ What are Western Disturbances?

Western Disturbances are weather systems (specifically extra-tropical cyclones) that bring rain, snowfall, and cloudy weather to north-western India, especially during winter.

🌍 Where do they come from?

  • They originate over the Mediterranean Sea.

  • These disturbances travel eastward with the jet stream winds (fast-moving winds in the upper atmosphere).

  • As they move towards India, they pass through:

    • Iran

    • Iraq

    • Afghanistan

    • Pakistan
      ... and finally reach northern India.

🌀 Why are they called “Disturbances”?

  • They disturb the calm weather and bring precipitation (rain/snow).

  • Since they come from the west, they’re called Western Disturbances.

☁️ What kind of weather do they bring?

  • Winter rain in Punjab, Haryana, Delhi, and western UP

  • Snowfall in Jammu & Kashmir, Himachal Pradesh, and Uttarakhand

  • Cloudy sky and drop in temperature in northern India

⛄ Importance of Western Disturbances

  1. Good for agriculture:

    • They bring winter rainfall that helps in growing rabi crops, especially wheat.

  2. Snowfall:

    • Essential for maintaining glaciers in the Himalayas, which feed rivers like the Ganga.

⚠️ Problems caused by Western Disturbances

  • Unseasonal rainfall can damage crops.

  • Sometimes lead to floods or landslides in hilly areas.

  • Cause cold waves after the rain/snow.

📅 When do they occur?

  • Mainly during winter and early summer (from November to March).

  • Sometimes they may affect pre-monsoon months too (April–May).

🌪️ Formation of Western Disturbances

🧊 1. Cold and Warm Air Interaction (Over Mediterranean)

  • In late autumn and winter, cold dry air from the polar regions moves southward.

  • At the same time, warm moist air from the subtropical region (near the Mediterranean) moves northward.

  • These two different air masses meet over areas like the Mediterranean Sea, Iran, and Iraq.

📌 This meeting of warm and cold air creates an unstable zone in the upper atmosphere.

🌬️ 2. Formation of an Extra-Tropical Cyclone

  • Due to the instability, a low-pressure system develops in the mid and upper troposphere (not on the surface like tropical cyclones).

  • This system is called an extra-tropical cyclone or mid-latitude cyclone.

📌 It rotates anti-clockwise in the northern hemisphere, just like low-pressure systems.

💨 3. Movement by Westerlies (Jet Streams)

  • In the upper atmosphere, strong winds called the westerly jet streams blow from west to east.

  • These jet streams pick up the cyclone and carry it eastward from the Mediterranean → through West Asia → towards India.

📌 The jet stream acts like a conveyer belt or highway for these disturbances.

💧 4. Moisture Collection Along the Path

  • While moving, the disturbance passes over seas and moist regions (like the Caspian Sea, Persian Gulf).

  • It collects moisture from these water bodies.

📌 This collected moisture will later fall as rain or snow when it hits the Himalayas or the plains of northern India.

🏔️ 5. Impact in India (Precipitation & Temperature Changes)

  • When the system reaches northern India, it hits the Himalayan barrier, which forces the moist air to rise.

  • This rising air cools and condenses, leading to:

    • Snowfall in the hills (J&K, Himachal, Uttarakhand)

    • Rainfall in the plains (Punjab, Haryana, Delhi, UP)

  • It also causes a drop in temperature after the rainfall.

📌 Important Features of the Western Disturbance System:

Feature Explanation
Type of System Extra-tropical (Not tropical like cyclones in Bay of Bengal)
Season Mainly winter (Nov to March)
Movement From west to east (via jet stream)
Weather Caused Rain, snow, cloud cover, cold wave
Source Region Mediterranean Sea
Affected Indian States Punjab, Haryana, Delhi, UP, J&K, HP, Uttarakhand

🔁 Summary (Revision points)

Point Info
Origin Mediterranean Sea
Travels through West Asia → Pakistan → North India
Weather caused Rain, snow, cloudy skies
Season Winter (Nov–March)
Affected areas J&K, HP, Punjab, Haryana, Delhi, UP
Benefit Rabi crops (especially wheat)
Harm Crop damage, floods, landslides, cold waves

UPSC MCQ'S:

1. Consider the following statements with reference to Western Disturbances (WD): 
  1.  These are anticyclonic circulations occurring at the stratospheric levels.
  2.  These are responsible for snowfall and fog in northern India. 
  3.  These carry moisture from the Mediterranean Sea. 
 Which of the statements given above is/are correct? 
 (a) 1 and 2 only 
 (b) 2 and 3 only 
 (c) 3 only 
 (d) 1, 2 and 3

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