Western Disturbances : Occurrence, Frequency and Impact on Weather

Western disturbances are defined as cyclonic storms that begin in western India and affect the entire country. According to the India Meteorological Department (IMD), a western disturbance is “cyclonic circulation in the mid and lower tropospheric levels or as a low-pressure area on the surface, which occur in middle latitude westerlies and originate over the Mediterranean Sea, Caspian Sea, and Black Sea and move eastwards across north India”. In practice, a western disturbance does not have to begin over the three seas or proceed into India.

When do Western Disturbances occur the most in a year

These storms are known to strike India most during the winter season(the period of December to February) and has the highest frequency. This shows that on an average 72 such storms pass over India every year from the 1950-2022.

  • Pre-monsoon Season (summer) during March-May.
  • Monsoon season June-September.
  • Post-monsoon season October-November.

How Western Disturbances Frequency Changed over time

Depending on the place and season analyzed, as well as the dataset utilized, western disturbances appear to have increased, declined, or shown no significant trend. To be sure, studies that have counted them using meteorological reports, which have primarily concentrated on the northwestern Himalayas and India’s northern states, have typically found a decline in frequency. However, their frequency increased significantly less in the winter season than in the monsoon or pre-monsoon seasons. Furthermore, increasing the frequency of western disturbances may not result in greater rain and snowfall if their intensity reduces.

Western Disturbances Impact on Weather

While there is no consensus on what is going on with western disturbances, it is easy to track the patterns in their effects. Rainfall in India’s northern states is the most significant influence of westem disturbances, and IMD has provided rain data for India since 1901. This demonstrates that the four northern states and union territories—Jammu & Kashmir, Ladakh, Himachal Pradesh, and Uttarakhand—have had somewhat varied winter precipitation trends. Over Himachal Pradesh and Uttarakhand.

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