Cyclones: A Comprehensive UPSC Prelims Guide
Category: GS-1 (Geography), GS-3 (Disaster Management, Environment, Climate Change)
1. What is a Cyclone?
A cyclone is a large-scale, low-pressure system with spiraling winds around a calm center called the eye. In the Indian Ocean region, these are called tropical cyclones and can vary from depressions to super cyclonic storms based on wind speed.
2. Types of Cyclones
- Tropical Cyclones: Develop over warm ocean waters (above 26.5°C), characterized by organized convection and rotating winds.
- Extra-Tropical Cyclones: Form in temperate regions, usually associated with fronts and cold weather systems.
- Tornadoes: Small but intense cyclonic storms occurring mainly on land.
3. Formation Conditions of Tropical Cyclones
- Sea surface temperature above 26.5°C.
- Pre-existing low-pressure area or disturbance.
- High humidity in lower and middle troposphere.
- Sufficient Coriolis force to initiate rotation (minimum 5° latitude from equator).
- Low vertical wind shear (strong shear disrupts development).
4. Structure of a Cyclone
- Eye: Calm, clear center with lowest pressure.
- Eyewall: Ring of towering thunderstorms surrounding the eye; highest wind speeds and heaviest rains.
- Rainbands: Spiral bands of clouds and precipitation extending outward.
5. Cyclone Seasons in the Indian Ocean
- Pre-Monsoon: April to June (cyclones develop over Bay of Bengal and Arabian Sea).
- Post-Monsoon: October to December (most intense cyclones occur in this period).
Note: Bay of Bengal accounts for ~80% of tropical cyclones in the Indian region; Arabian Sea cyclones are less frequent but can be very severe.
6. Classification of Cyclones by IMD
| Category | Wind Speed (km/h) | Description |
|---|---|---|
| Depression | 31–50 | Weak cyclonic circulation |
| Deep Depression | 51–62 | Stronger winds, heavier rains |
| Cyclonic Storm | 63–88 | Moderate intensity cyclone |
| Severe Cyclonic Storm | 89–117 | Strong winds, heavy rains |
| Very Severe Cyclonic Storm | 118–166 | Very intense cyclone |
| Extremely Severe Cyclonic Storm | 167–221 | Extremely strong cyclone |
| Super Cyclonic Storm | ≥222 | Most destructive cyclones |
7. Impact of Cyclones
- Human Casualties and Displacement: Flooding and strong winds cause loss of lives and displacement.
- Agricultural Loss: Crop damage due to flooding, saltwater intrusion.
- Infrastructure Damage: Roads, communication networks, power supply disruptions.
- Environmental Effects: Coastal erosion, mangrove destruction, impact on marine life.
8. Storm Surge
A storm surge is a sudden rise in sea level caused by strong cyclone winds pushing seawater toward the coast, leading to severe coastal flooding. It is responsible for most deaths during coastal cyclones.
9. Cyclone Monitoring & Forecasting in India
- IMD's Role: Uses satellites (INSAT series), Doppler radar, ocean buoys, and numerical models.
- International Cooperation: Collaborates with WMO, NOAA, and other countries for better tracking.
- Early Warning Dissemination: Alerts issued to governments and public via media, apps, SMS.
10. Disaster Preparedness and Management
- Evacuation: Large-scale evacuation of coastal populations to cyclone shelters.
- Infrastructure: Building cyclone-resistant homes, embankments, and mangrove restoration.
- Post-Disaster Relief: Medical aid, food, water supply, and rehabilitation programs.
11. Climate Change and Cyclones
Climate change has increased sea surface temperatures and may lead to more frequent and intense cyclones. There is evidence of longer cyclone seasons and higher rainfall rates within cyclones. Coastal vulnerability is amplified due to rising sea levels.
12. Recent & Current Affairs Highlights (2024-25)
- 2024 Odisha Cyclone Preparedness: After Cyclone Sitrang, Odisha enhanced its early warning systems and mangrove afforestation as a natural buffer.
- Bay of Bengal Warming: Recent studies show Bay of Bengal warming faster than Arabian Sea, increasing cyclone intensity risk.
- Satellite Launch: India launched 'INSAT-3DS' satellite with improved cyclone monitoring sensors in 2024.
- Disaster Resilience Initiatives: National Cyclone Risk Mitigation Project Phase II focuses on vulnerable coastal districts with international funding.
13. Important UPSC Prelims Questions (PYQs) Related to Cyclones
- Q: What causes the rotation of tropical cyclones?
Answer: Coriolis force. - Q: Which ocean basin generates the highest number of cyclones affecting India?
Answer: Bay of Bengal. - Q: What is a storm surge?
Answer: Rise in sea level caused by strong winds and low pressure. - Q: During which months does the Bay of Bengal witness the highest frequency of cyclones?
Answer: October to December. - Q: Which Indian state is most vulnerable to cyclones?
Answer: Odisha.
14. Interactive MCQs for Revision
15. Summary
- Cyclones form over warm tropical oceans and cause massive destruction via strong winds and floods.
- Bay of Bengal is the most cyclone-prone region affecting India.
- IMD's monitoring and early warnings have reduced casualties in recent years.
- Climate change is likely to increase the intensity and frequency of cyclones.
- Understanding cyclone dynamics and management is critical for UPSC prelims and mains.
