Odisha, A.P. brace for storm as low pressure intensifies

Why in news?

IMD expects a Bay of Bengal low-pressure system to intensify into a severe cyclone, crossing south Odisha-north Andhra coast.

UPSC Relevance  

Prelims: Formation of tropical cyclones, IMD classification, storm surge, cyclone naming, colour-coded warnings, NDRF/ODRAF

Mains: 

GS1 – Important geophysical phenomena such as cyclones; Salient features of world’s physical geography. GS3 – Disaster and disaster management.

What is a Tropical Cyclone?

A tropical cyclone is an intense low-pressure system that forms over warm tropical oceans. Winds spiral inwards towards the centre at high speed – anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

• Local names: Cyclones (Indian Ocean), hurricanes (Atlantic and East Pacific), typhoons (West Pacific), willy-willies (Australia).
• Energy source: Latent heat released when moist air rises and condenses into clouds. This is why cyclones weaken quickly after landfall – they lose their supply of moisture.

Conditions needed for formation

• Warm sea: Sea surface temperature above about 26.5°C, extending to a depth of around 50 metres.
• Coriolis force: Needed to start the spin. This is why cyclones rarely form within about 5° of the equator.
• Low vertical wind shear: Small difference in wind speed between lower and upper atmosphere, so the system can grow vertically.
• Pre-existing disturbance: A low-pressure area or trough to begin with.
• Moist air and upper divergence: Humid mid-troposphere and outflow of air at the top keep the system going.

Structure

• Eye: Calm, clear centre with lowest pressure, usually 20-50 km wide.
• Eye wall: Ring of tall clouds around the eye with the strongest winds and heaviest rain.
• Rain bands: Spiral bands of clouds and rain extending hundreds of kilometres outward.
• Landfall: When the centre (eye) of the cyclone crosses the coast.

IMD Classification of Low-Pressure Systems

Note: Wind speed here means maximum sustained surface wind. A system gets a name only once it reaches cyclonic storm stage.

Why is the Bay of Bengal More Cyclone-Prone?

• Seasons: Two peaks – pre-monsoon (April-May) and post-monsoon (October-December). The post-monsoon season, like now, produces many of the strongest Bay of Bengal cyclones.
• Climate change: Warmer seas are causing rapid intensification – a storm can jump several categories within 24 hours, cutting warning time. Arabian Sea cyclones have become more frequent and intense.

Hazards from a Cyclone

• Storm surge: Abnormal rise of sea level pushed onto the coast by strong winds and low pressure. It is the biggest killer in cyclones. Shallow coasts and high tide make it worse.
• Strong winds: Damage to kutcha houses, power lines, telecom towers, trees and crops.
• Very heavy rainfall: Leads to river and urban flooding and landslides inland – like the expected rain in Andhra’s Alluri Sitharama Raju district.
• After-effects: Salinity in farmland, loss of livelihood for fishers, disease outbreaks and disruption of supply chains.

Cyclone Warning System in India

• IMD: Nodal agency. Its Regional Specialised Meteorological Centre (RSMC), New Delhi, gives advisories to 13 countries of the North Indian Ocean.
• Tools: INSAT-3D/3DR satellites, Doppler Weather Radars along the coast, ocean buoys and numerical weather prediction models.

Four-stage cyclone warning

• Colour codes: Green (no action), Yellow (be updated), Orange (be prepared), Red (take action).
• Naming: Done by the WMO/ESCAP Panel on Tropical Cyclones. Its 13 member countries submitted 13 names each; the 2020 list has 169 names, used in order. A name is never repeated.

Disaster Management – The Odisha Model

• Lesson from 1999: The Odisha Super Cyclone killed around 10,000 people. Odisha then set up the Odisha State Disaster Management Authority (OSDMA) in 1999 – before the national law – and the ODRAF.
• Zero-casualty approach: Large-scale early evacuation, about a million people for Phailin (2013) and over a million for Fani (2019). Deaths fell sharply and the UN praised Odisha’s efforts.
• Infrastructure: Hundreds of multi-purpose cyclone shelters, managed by village committees and used as schools in normal times.
• Community role: Village-level task forces, mock drills, and siren towers along the coast for last-mile warning.

Challenges

• Landfall uncertainty – as in this case, a stretch from West Godavari to Srikakulam is possible, making evacuation planning hard.
• Rapid intensification leaves less time to act.
• Inland flooding and damage after landfall get less attention than coastal preparedness.
• Vulnerable groups – fishers, migrant workers, the elderly – and weak kutcha housing.
• Long recovery for power, water, roads and livelihoods; uneven preparedness across States.

Way Forward

• Impact-based forecasting – telling people what the storm will do (flooding, house damage), not just wind speed.
• Expand cyclone shelters and ensure they are accessible for women, children, the elderly and the disabled.
• Underground power cabling and stronger housing codes in coastal districts.
• Restore mangroves and coastal shelter belts; strengthen embankments.
• Insurance and quick compensation for fishers and farmers; replicate the Odisha model in other coastal States.

Practice MCQ

Q1. Consider the following statements about tropical cyclones:

1. They rarely form within about 5° of the equator because the Coriolis force there is too weak.

2. In the Northern Hemisphere, winds around a tropical cyclone rotate in a clockwise direction.

3. A sea surface temperature of about 26-27°C or more is needed for their formation.

How many of the statements given above are correct?

(a) Only one        (b) Only two        (c) All three        (d) None

Answer: (b)  Statement 2 is incorrect: cyclones rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Mains Practice Question

Q. Why is the east coast of India more prone to tropical cyclones than the west coast? Examine how Odisha’s approach to cyclone management can serve as a model for other coastal States in the context of rapidly intensifying cyclones. (15 marks, 250 words)

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