Deep Depression And Western Disturbance
Source: Indian Express
GS I: Geography- Climatology, GS III: Disaster Management
Overview
- Uttar Pradesh received 66.5 mm of rainfall against the normal 7.6 mm, with 56 districts recording excess rainfall, resulting in casualties and property damage.
- The deep depression, originating over the Bay of Bengal, moved inland and weakened into a well-marked low-pressure area while continuing to produce rainfall.
- The interaction between the deep depression and a Western Disturbance intensified rainfall, accompanied by strong winds and thunderstorms over parts of the state.
- The event highlights the need for improved weather forecasting, early warning systems, flood management and climate-resilient infrastructure to reduce the impact of extreme rainfall.
Why in the News?
Uttar Pradesh experienced intense rainfall over a three-day period due to the likely interaction between a deep depression over central India and a Western Disturbance (WD), resulting in flooding, damage to houses and casualties across several districts.
News in Brief
- Uttar Pradesh received 66.5 mm of rainfall against the normal 7.6 mm during the period, while 56 of the state’s 75 districts recorded excess rainfall.
- The intense rainfall led to at least 62 deaths, 46 injuries and damage to over 1,000 houses.
- According to the India Meteorological Department (IMD), the interaction between a deep depression and a Western Disturbance intensified rainfall over parts of Uttar Pradesh.
- The southwest monsoon continued to withdraw across northwestern India even as these weather systems brought heavy to very heavy rainfall to the region.
Depp Depression and Its Role
- A deep depression is an intensified low-pressure weather system that can produce widespread rainfall, strong winds and flooding.
- The deep depression originated over the Bay of Bengal and crossed the North Andhra Pradesh-South Odisha coast before weakening.
- It moved inland and became centered over parts of north-eastern Madhya Pradesh and south-eastern Uttar Pradesh.
- The system drew warm, moisture-laden air towards its centre, where the air rose, cooled and condensed, resulting in cloud formation and rainfall.
Mechanism of rainfall:
- Localized heating creates a low-pressure area as warm air rises.
- Moist air moves towards the low-pressure centre from surrounding regions.
- The incoming air rises, cools and condenses to form clouds and precipitation.
- As the depression weakens, wind speeds and rainfall intensity generally decline.
According to the IMD, the depression moved northwestwards on Sunday and weakened into a well-marked low-pressure area. It was expected to continue moving in the same direction across Uttar Pradesh.
Role of the Western Disturbance
A Western Disturbance is an extra-tropical weather system that originates beyond the Indian subcontinent and moves eastwards towards India.
Origin and Movement
- Western Disturbances generally originate over the Mediterranean Sea and adjoining regions, including the Black Sea and Caspian Sea.
- They are eastward-moving, rain-bearing weather systems associated with low-pressure areas and interactions between polar and tropical air masses.
- They travel towards north-western India under the influence of the subtropical westerly jet stream.
Subtropical Westerly Jet Stream
- The subtropical westerly jet stream is a high-altitude, fast-moving air current flowing from west to east in the upper atmosphere.
- It carries Western Disturbances towards the Himalayan and Tibetan highlands.
- As moisture-laden Western Disturbances interact with the Himalayas, they produce cloudy weather, rainfall, thunderstorms and, in higher elevations, snowfall.
- Their influence is particularly significant over north and north-western India.
The IMD identified the presence of a Western Disturbance high in the atmosphere as a trough, or an elongated zone of relatively low pressure, over north-western India.
Interaction Between the Two Weather Systems
- The simultaneous presence of the deep depression and the Western Disturbance created conditions for intense rainfall over Uttar Pradesh.
- The deep depression transported moisture and generated widespread rainfall over central and northern India.
- The Western Disturbance contributed additional atmospheric instability and supported the development of strong convective activity.
- Their interaction was associated with strong gusty surface winds and heavy to very heavy rainfall in some areas.
- As the depression weakened into a well-marked low-pressure area, the overall rainfall intensity was expected to decline.
The episode demonstrates that rainfall intensity depends not only on an individual weather system but also on the interaction of multiple systems, moisture availability and atmospheric circulation.
Significance and Implications
- Disaster management- Heavy rainfall over a short period can overwhelm drainage systems, cause urban flooding and disrupt transport and essential services.
- Agriculture– Excess rainfall may damage standing crops, cause waterlogging and affect harvesting activities.
- Climate and weather forecasting- Interactions between tropical and extra-tropical systems complicate rainfall prediction and require continuous meteorological monitoring.
- Monsoon variability- Heavy rainfall during the withdrawal phase highlights that the retreat of the southwest monsoon does not necessarily mean an immediate end to rainfall.
Important Concepts
|
Term |
Explanation |
|---|---|
|
Depression |
A low-pressure weather system with organized circulation and stronger winds than an ordinary low-pressure area. |
|
Deep Depression |
A more intense stage of a tropical low-pressure system, associated with stronger winds and heavy rainfall. |
|
Western Disturbance |
An eastward-moving extra-tropical weather system that brings winter rainfall to north-western India and can influence weather in other seasons. |
|
Monsoon Withdrawal |
The gradual retreat of the southwest monsoon from north-western India towards the southern peninsula. |
|
Atmospheric Trough |
An elongated region of relatively low atmospheric pressure that can support cloud formation and rainfall. |
Way Forward and Conclusion
Strengthening IMD forecasting and early warning systems, improving urban drainage and flood management, and promoting climate-resilient agriculture are essential to minimize the impact of extreme rainfall.
An integrated approach combining accurate weather prediction, disaster preparedness and resilient infrastructure is crucial to protect lives, livelihoods and agricultural productivity.
UPSC Prelims and Mains Practice Question
With reference to Western Disturbances, consider the following statements:
- They are extra-tropical weather systems that generally originate over the Mediterranean region and adjoining areas.
- They move towards India under the influence of the subtropical westerly jet stream.
- They are responsible for the southwest monsoon rainfall over the entire Indian subcontinent.
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only.
Mains Practice Question
Q) Explain how the interaction between tropical depressions and Western Disturbance can intensify rainfall over northern India. Discuss the challenges associated with forecasting and managing such extreme weather events. (150 words)
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