1. Introduction: India is highly vulnerable to natural hazards especially earthquakes, floods, drought, cyclones and landslides. Studies indicate that natural disaster losses equate to up to 2% of India’s Gross Domestic Product (GDP) and up to 12% of Central government revenue. The cyclones that occur between Tropics of Cancer and Capricorn are known as Tropical Cyclones. Tropical cyclones are weather systems in which winds equal or exceed gale force (minimum of 34 knot, i.e., 62 kmph).
Indian sub-continent is the worst affected region of the world, having a coast line of 7516 kms. (5400 kms along the mainland, 132 kms in Lakshadweep and 1900 kms in Andaman and Nicobar Islands) is exposed to nearly 10% of the world’s Tropical Cyclones. There are 13 coastal states/UTs encompassing 84 coastal districts which are affected by cyclones (Fig. 1). Four States (Andhra Pradesh, Odisha, Tamil Nadu and West Bengal) and one UT (Pondicherry) on the East Coast and One State (Gujarat) on the West Coast are more vulnerable to cyclone disasters. 40% of the total population lives within 100 km of coastline. Analysed data for the period 1980-2000 shows that on an average, annually 370 million people are exposed to cyclones in India. Cyclones occur in the month of May-June and October-November, with primary peak in November and secondary peak in May.
Although cyclones affect the entire coast of India the East Coast is more prone compared to the West Coast. An analysis of the frequencies of cyclones on the East and West coasts of India during 1891-2000 show that nearly 308 cyclones (out of which 103 were severe) affected the East Coast. During the same period 48 tropical cyclones crossed the West Coast, of which 24 were severe cyclonic storms. Out of the cyclones that develop in the Bay of Bengal, over 58 percent approach and cross the East Coast in October and November. Only 25 % of the cyclones that develop over the Arabian Sea approach the West Coast. In the pre-monsoon season, corresponding figures are 25 percent over Arabian sea and 30 percent over Bay of Bengal.
Recurring cyclones account for large number of deaths, loss of livelihood opportunities, loss of public and private property and severe damage to infrastructure, thus seriously reversing the developmental gains at regular intervals. Broad scale assessment of population at risk suggests that an estimated 32 crore people, which accounts for almost third of the country’s total population, are vulnerable to cyclone related hazards. Climate change and its resultant sea-level rises can significantly increase the vulnerability of coastal population.
2. Classification of Tropical Cyclones: The criteria followed by Meteorological Department of India (IMD) to classify the low pressure systems in the Bay of Bengal and in the Arabian Sea as adopted by World Meteorological Organisation (WMO) are as under:
Type of Disturbances | Associated Wind Speed in the Circulation |
Low pressure Area | Less than17 knots (<31 kmph) |
Depression | 17 to 27 knots (31 to 49 kmph) |
Deep Depression | 28 to 33 knots (50 to 61 kmph) |
Cyclonic Storm | 34 to 47 knots (62 to 88 kmph) |
Severe Cyclonic Storm | 48 to 63 knots (89 to 118 kmph) |
Very Severe Cyclonic Storm | 64 to 119 knots (119 to 221 kmph) |
Super Cyclonic Storm | 120 knots and above (222 kmph and above) |
3. Major Tropical Cyclones in Indian Sub-continent: The major Tropical cyclones which struck the coastal districts in India during the period 1891-2006 are as under:
WEST COAST | EAST COAST |
State | Coastal Districts | No. of Cyclones. | State | Coastal Districts | No. of Cyclones. |
Kerala (3) | Malappuram | 1 | West Bengal (69) | 24 Paragana (North and South). | 35 |
Kozikode | 1 | Midnapur | 34 |
Kannur | 1 |
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Karnataka (2) | Dakshina Kannada | 1 | Odisha (98) | Balasore | 32 |
Uttar Kannada | 1 | Cuttack | 32 |
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| Puri | 19 |
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| Ganjam | 15 |
Maharashtra (13) | Sindhudurg | 3 | Andhra Pradesh (79) | Srikakulam | 14 |
Ratnagiri | 3 | Vishakhapatnam | 9 |
Mumbai | 3 | East Godavari | 8 |
Thane | 4 | West Godavari | 5 |
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| Krishna | 15 |
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| Guntur | 5 |
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| Prakasam | 7 |
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| Nellore | 16 |
Goa (2) | Goa | 2 | Tamil Nadu (54) | Chennai | 18 |
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| Cuddalore | 7 |
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| Southarcot | 5 |
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| Tanjavur | 12 |
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| Pudukkottal | 5 |
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| Ramnathpuram | 3 |
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| Tirunelveli | 2 |
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| Kanyakumari | 2 |
Gujarat (28) | Surat | 1 | Pondicherry (8) | Pondicherry (UT) | 8 |
Kaira | 1 |
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Bhavnagar | 4 |
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Amereli | 4 |
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Junangarh | 7 |
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Jamnagar | 6 |
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Kachchh | 5 |
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4. Destruction caused by Cyclones: There are three elements associated with cyclones which cause destruction during its occurrence. These are:
Strong Winds/Squall: Cyclones are known to cause severe damage to infrastructure through high speed winds. Very strong winds which accompany a cyclonic storm damages installations, dwellings, communications systems, trees etc., resulting in loss of life and property. Gusts are short but rapid bursts in wind speed are the main cause for damage. Squalls on the other hand, are longer periods of increased wind speed and are generally associated with the bands of thunderstorms that make up the spiral bands around the cyclone.
Torrential rains and inland flooding: Torrential rainfall (more than 30 cm/hour) associated with cyclones is another major cause of damages. Unabated rain gives rise to unprecedented floods. Rain water on top of the storm surge may add to the fury of the storm. Rain is a serious problem for the people which become shelter less due to cyclone. Heavy rainfall from a cyclone is usually spread over wide area and cause large scale soil erosion and weakening of embankments.
Storm Surge: A Storm surge can be defined as an abnormal rise of sea level near the coast caused by a severe tropical cyclone; as a result of which sea water inundates low lying areas of coastal regions drowning human beings and life stock, causes eroding beaches and embankments, destroys vegetation and leads to reduction of soil fertility.
Brief details about damages caused by wind of different speed during cyclones are as under
Wind Speed Intensity | Damages expected. |
Low Pressure Area | Less than 17 knots (<31 kmph) |
Depression | 17 to 27 knots (31 to 49 kmph) |
Deep Depression | 28 to 33 knots (50 to 61 kmph) |
Cyclonic Strom | 34 to 47 knots (62 to 88 kmph) |
Severe Cyclonic Strom | 48 to 63 knots (89 to 118 kmph) |
Very Severe Cyclonic Strom | 64 to 119 knots (119 to 221 kmph) |
Super Cyclonic Strom | 1120 knots and above (222kmph and above) |
Benefits of Tropical Cyclones: Although Tropical cyclones are known for destruction they cause, when they strike they also bestow certain benefits to the climatic conditions of that area such as
Relieve drought conditions.
Carry heat and energy away from the tropics and transport it towards temperate latitudes, thus helps to maintain equilibrium in the Earth’s troposphere and
Maintain a relatively stable and warm temperature worldwide.
Management of Cyclones: There are many structural and non-structural measures for effective disaster management of cyclones. The structural measures include construction of cyclone shelters, construction of cyclone resistant buildings, road links, culverts, bridges, canals, drains, saline embankments, surface water tanks, communication and power transmission networks etc. Non-structural measures like early warning dissemination systems, management of coastal zones, awareness generation and disaster risk management and capacity building of all the stakeholders involved. These measures are being adopted and tackled on State to State basis under National Cyclone Risk Mitigation Project (NCRMP) being implemented through World Bank Assistance.