Source: NDTV
Subject: Geography
Context: The India Meteorological Department (IMD) has issued an alert for a quick succession of two Western Disturbances (WD) expected to sweep across Northwest and Central India from January 31 to February 3, 2026.
About Western Disturbance:
What is a Western Disturbance?
- A Western Disturbance (WD) is an extra-tropical storm (or low-pressure system) that originates in the Mediterranean region.
- It travels eastwards across the Middle East, Iran, Afghanistan, and Pakistan before entering the Indian subcontinent.
Origin:
- The Mediterranean Sea, often fueled by moisture from the Caspian and Black Seas.
Formation
- A high-pressure area over Europe (near Ukraine) pushes cold polar air toward the relatively warmer, moist air over the Mediterranean.
- This interaction creates an extratropical depression (a non-tropical storm).
- These storms are then pushed toward India by the Subtropical Westerly Jet Stream, a high-altitude wind current acting as a global conveyor belt.
- Upon hitting the Himalayan barrier, the moisture-laden air is forced to rise, leading to condensation and precipitation.
Impact of Western Disturbances on India:
Winter Precipitation:
- WDs are the primary source of non-monsoonal rainfall in India.
- They bring heavy snowfall to the Western Himalayas (J&K, Himachal, Uttarakhand) and light to moderate rain to the plains (Punjab, Haryana, Delhi, UP).
Agricultural Boon and Bane:
- Boon for Rabi Crops: The winter showers are essential for Wheat, Mustard, and Gram (Chana). It provides natural irrigation during the dry winter months.
- Bane for Farmers: Intense WDs can cause hailstorms and thunderstorms, which damage standing crops. The IMD has recently advised farmers to drain excess water to prevent root rot.
Temperature & Cold Waves
- Before Arrival: Night temperatures usually rise due to cloud cover trapping heat (greenhouse effect).
- After Departure: As the sky clears, cold northerly winds from the snow-clad mountains rush into the plains, leading to a sharp drop in temperature and dense fog, triggering Cold Wave conditions.
Water Security: Snowfall from WDs feeds the Himalayan glaciers, which are the source of perennial rivers like the Ganga, Yamuna, and Indus, ensuring water availability during the summer.
