Context
Over the past six months, variations in the intensity and locations of western disturbances have brought heavy rainfall to Delhi during some months, and kept the city dry and in the grip of a heat wave at other times.
What is Western Disturbance?
- A western disturbance is an extratropical storm originating in the Mediterranean region that brings sudden winter rain to the northern parts of the Indian subcontinent.
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In the term “extra-tropical storm”, storm refers to low pressure. “Extra-tropical" means outside the tropics.
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- A Western Disturbance is a low-pressure area or a trough over the surface or the upper-air in the westerly winds regime, north of 20 degrees north, causing changes in pressure, wind pattern and temperature fields.
- It is accompanied by cloudiness, with or without precipitation.
- Western Disturbances are at their peak in January and February and are considered important for the development of rabi crops in the Northern subcontinent.
- The disturbance travels from the “western” to the eastern direction.
- 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.
Low Pressure Area
- A low is an area where air pressure is lower than it is in the areas surrounding it.
- Air near the surface flows down and away in a high pressure system (left) and air flows up and together at a low pressure system (right).
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Impact
- The Western Disturbances are not always the harbingers of good weather.
- 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.
