Tropical Cyclones and Other Atmospheric Hazards

What a tropical cyclone is

A tropical cyclone is an intense, rotating low-pressure storm that forms over warm tropical oceans, with winds spiralling inward and upward around a calm centre. The same phenomenon has different local names: cyclones in the Indian Ocean, hurricanes in the Atlantic and eastern Pacific, typhoons in the western Pacific and China Sea, and willy-willies in north-western Australia. Winds rotate anticlockwise in the northern hemisphere and clockwise in the southern hemisphere because of the Coriolis force. GS Paper 1 lists cyclones among important geophysical phenomena, and their impact on India's long eastern coast makes them a regular topic in Mains and Prelims.

Conditions needed for formation

1. Warm sea surface – at least about 26–27°C down to a depth of about 50–60 metres, to supply heat and moisture.
2. Coriolis force strong enough to start rotation – so cyclones rarely form within about 5° of the equator, where the force is nearly zero.
3. Low vertical wind shear – winds that do not change much with height, so the storm's tall column can stay upright.
4. A pre-existing low-pressure disturbance or weak vortex.
5. Upper-level divergence – outflow of air at the top of the storm, which keeps surface pressure falling.
6. A moist mid-troposphere.

Structure of a cyclone

A cyclone weakens over land (landfall) or cold water because it loses its supply of heat and moisture and faces more friction.

Life cycle and energy

Cyclones are powered by latent heat of condensation: warm, moist air rises, its water vapour condenses into clouds and releases heat, which warms the air further and makes it rise faster, drawing in more moist air at the surface. This self-reinforcing loop – sometimes called a "heat engine" – lets a weak low deepen rapidly. Rapid intensification (a jump in wind speed of about 55 km/h or more within 24 hours) is becoming more common as oceans warm; Cyclone Ockhi (2017) and Tauktae (2021) both intensified fast.

IMD classification (North Indian Ocean)

The India Meteorological Department (IMD), New Delhi is the Regional Specialised Meteorological Centre (RSMC) for tropical cyclones over the North Indian Ocean. Names are chosen in advance from a list contributed by 13 countries of the WMO/ESCAP panel (Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE and Yemen); names are used in order and never repeated.

Cyclones and India

India has a coastline of over 11,000 km and is exposed to about 8 per cent of the world's tropical cyclones. The Bay of Bengal produces many more cyclones than the Arabian Sea – roughly four to one – because it is warmer, receives remnant typhoons from the Pacific, has weaker wind shear and a shallow, funnel-shaped coast that amplifies storm surges. Odisha, Andhra Pradesh, West Bengal and Tamil Nadu are the most exposed states; Gujarat is the most exposed on the west coast. Cyclones peak in two seasons: April–June (pre-monsoon) and October–December (post-monsoon), with October–November the most intense.

Recent studies show the Arabian Sea is warming fast and producing more and stronger cyclones – Kyarr (2019), Tauktae (2021) and Biparjoy (2023), one of the longest-lived in the region.

Major cyclones affecting India:

• Odisha super cyclone (1999) – about 10,000 deaths; triggered reforms.
• Phailin (2013) – Odisha evacuated about 10 lakh people; deaths were limited to a few dozen.
• Hudhud (2014) – Visakhapatnam.
• Fani (2019) – a rare summer extremely severe storm in Odisha; praised by the UN for evacuation.
• Amphan (2020) – super cyclone over the Bay; heavy damage in West Bengal and Bangladesh.
• Michaung (2023) – floods in Chennai; Dana (2024) in Odisha.

Hazards caused by cyclones

• Storm surge – an abnormal rise in sea level pushed by winds and low pressure; the deadliest aspect, responsible for most cyclone deaths.
• Strong winds that flatten houses, trees, power lines and crops.
• Torrential rain leading to floods and landslides inland.
• Saltwater intrusion into farmland and drinking water.

India's cyclone preparedness

• Early warning: IMD's four-stage warnings (pre-cyclone watch, cyclone alert, cyclone warning, post-landfall outlook), Doppler weather radars and satellites (INSAT-3D/3DR, 3DS).
• National Cyclone Risk Mitigation Project (NCRMP) with the World Bank – multipurpose cyclone shelters, evacuation roads, underground cabling, saline embankments.
• Odisha model – community-based shelters run by local volunteers, zero-casualty targets, and the Odisha State Disaster Management Authority, the first of its kind (1999).
• Coastal ecosystems – mangroves in the Sundarbans and Bhitarkanika, and coastal shelterbelts of casuarina, reduce surge and wind damage.
• Common Alerting Protocol (CAP) – location-based SMS warnings.

Other atmospheric hazards

• Thunderstorms and lightning: lightning kills more people in India than any other natural hazard in most years (around 2,500–3,000 deaths a year). States like Bihar, Odisha, Jharkhand and Madhya Pradesh are worst hit; the Damini app gives lightning alerts.
• Heatwaves: IMD declares a heatwave when maximum temperature is at least 40°C in the plains and 4.5–6.4°C above normal; 2024 saw record-long heatwaves in north India. Heat Action Plans, first started in Ahmedabad (2013), are now in many cities.
• Cold waves and fog in the north in winter disrupt transport.
• Cloudbursts – very heavy rain over a small area (about 10 cm or more in an hour over 20–30 sq km), common in the Himalaya; they cause flash floods such as Kedarnath (2013) and incidents in Himachal Pradesh in 2023–25.
• Dust storms in north-west India in May–June.
• Extra-tropical cyclones (temperate cyclones), which form along fronts in mid-latitudes, are different: they are larger, have no eye, form over land and sea, and bring the western disturbances to India.

Climate change and the future of cyclones

Scientists expect the total number of tropical cyclones worldwide to stay similar or fall slightly as the climate warms, but the share of very intense storms to rise, along with heavier rainfall and higher storm surges riding on a higher sea level. Cyclones are also tending to slow down near coasts, dumping more rain in one place, and to intensify rapidly just before landfall, which shortens warning time. For India this means that evacuation alone is not enough; housing standards, coastal zoning, drainage in cities such as Chennai, Kolkata and Mumbai, crop insurance and quick restoration of power and telecom matter as much. The Sendai Framework (2015–2030) and India's Prime Minister's Ten-Point Agenda on Disaster Risk Reduction (2016) stress this shift from relief to risk reduction and resilience.

Mains practice question

Why does the Bay of Bengal experience more tropical cyclones than the Arabian Sea? Evaluate India's preparedness in reducing cyclone deaths, with examples. (250 words)

Answer framework

• Intro: definition; India's exposure.
• Reasons: warmer SST, Pacific remnants, low shear, shallow funnel coast; but Arabian Sea warming.
• Preparedness: IMD as RSMC, warnings, NCRMP shelters, Odisha model, mangroves, CAP.
• Results: 1999 vs Phailin, Fani.
• Gaps: livelihoods, housing, rapid intensification.