Western Disturbances (WD)

Why in News?

• The daytime’s temperatures in Delhi were recently above normal in December 2022 because of fewer  Western Disturbances (WD).

Highlights

• Western disturbances are storms that originate in the Caspian or Mediterranean Sea, and bring non-monsoonal rainfall to northwest India, according to the India Meteorological Department (IMD).
• A Western Disturbance, labelled as an extra-tropical storm originating in the Mediterranean, is an area of low pressure that brings sudden showers, snow and fog in northwest India.
• The disturbance travels from the “western” to the eastern direction.
• These travel eastwards on high-altitude westerly jet streams – massive ribbons of fast winds traversing the earth from west to east.
• They gradually travel across the middle-east from Iran, Afghanistan and Pakistan to enter the Indian sub-continent.
• Disturbance means an area of “disturbed” or reduced air pressure.
• Equilibrium exists in nature due to which the air in a region tries to normalise its pressure.
• A WD is associated with rainfall, snowfall and fog in northern India. It arrives with rain and snow in Pakistan and northern India.
• The moisture whichh WDs carry with them comes from the Mediterranean Sea and/or from the Atlantic Ocean.
• WD brings winter and pre-monsoon rain and is important for the development of the Rabi crop in the Northern subcontinent.
• The WDs are not alwayss the harbingers of good weather. Sometimes WDs can cause extreme weather events like floods, flash floods, landslides, dust storms, hail storms and cold waves killing people, destroying infrastructure and impacting livelihoods.
• During the summer months of April and May, they move across North India and at times help in the activation of monsoon in certain parts of northwest India.
• During the monsoon season, western disturbances may occasionally cause dense clouding and heavy precipitation.
• Weak western disturbances are associated with crop failure and water problems across north India.
• Strong western disturbances can help residents, farmers and governments avoid many of the problems associated with water scarcity.