Updated on 14 May, 2019
Some recent Tropical cyclones in Indian Oceans
- In 2000, Tropical cyclone Elina struck the Mozambique, as a most devastating cyclone.
- In March, tropical cyclone Idai made headlines as one of the most severe storms to have made landfall in Mozambique accounting for nearly 1000 deaths.
- After Idai, Mozambique and Tanzania were struck by tropical cyclone Kenneth, a category 4 tropical cyclone that made landfall.
- Recently another major Tropical cyclone Fani, a tropical cyclone on the border of Category 5 intensity wind speeds, hit the east coast of India.
Basics of Tropical Cyclones Cyclones are caused by atmospheric disturbances around a low-pressure area distinguished by swift and often destructive air circulation. Cyclones are usually accompanied by violent storms and bad weather. Cyclones have been named differently as per the different regions of the world –
- In the China Sea and Pacific Ocean, they are known as typhoons;
- In the Caribbean Sea and Atlantic Ocean, they are known as hurricanes;
- In the Guinea lands of West Africa and southern USA, they are known as tornados;
- In north-western Australia they are known as willy-willies and
- In Indian Ocean they are known as tropical cyclones
Tropical cyclones are developed in the regions between the Tropics of Capricorn and Cancer. Conditions for formation of tropical cyclones To undergo tropical cyclogenesis, there are several favorable pre cursor environmental conditions that must be in place:
- It requires warm ocean waters of at least 26.5°C [80°F]) throughout a sufficient depth, at least on the order of 50 m. Warm waters are necessary to fuel the heat engine of the tropical cyclone.
- Tropical cyclones need to form at least five degrees of latitude away from the equator. It is because Coriolis force that is required for cyclones rotation is absent at equators. During a tropical cyclone, the Coriolis force deflects winds blowing towards the low-pressure center of the storm and creates circulation.
- Tropical Cyclones also require low wind shear to form. Wind shear is the change in wind speed or direction with height in the atmosphere. High wind shear will slow spinning cyclones down and prevent them from lasting a long time.
- High relative humidity in the atmosphere up to a height of about 5,000 metres.
- Atmospheric instability that encourages the formation of massive vertical cumulus clouds due to condensation of rising moist air.
Within the cyclone field, strong winds blow around the low-pressure centre in an anticlock-wise direction in the Northern Hemisphere and clockwise. Classifications of Cyclones in India In India, cyclones are classified based on:
- Strength of associated winds,
- Storm surges
- Exceptional rainfall occurrences
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: [caption id="attachment_10326" align="aligncenter" width="300"] Tropical Cyclones[/caption]
Criticisms of the classification mechanism of tropical cyclones Ranking of cyclones are done on the basis of Saffir Simpson classification. But it is not a proper method to measure the devastation, due to the following problems:
- First, it doesn’t take the flooding potential into account. Lower-lying, relatively flat areas are more prone to flooding than higher elevation regions or those with rugged topography.
- Second, it can’t take the characteristics of the location of landfall into consideration. The higher the population density of an area, the more people are at threat of losing their life, their homes and livelihoods.
This is why Idai and Eline resulted in far greater losses and fatalities than the stronger intensity Kenneth. Read Also: Critical Analysis of Coastal Regulation Zone (CRZ)
How Cyclones cause destructions?
Cyclones do not cause destruction directly but there the elements associated with them that cause the major part of destruction:
- Strong Winds/Squall: Very strong winds which accompany a cyclonic storm damages installation, dwellings, communications systems, trees etc., resulting in loss of life and property.
- 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
- 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.
Cyclone Prone areas of India Source -IMD Cyclones in Bay of Bengal and Arabian Sea The Indian subcontinent experiences cyclones from two basins: The Bay of Bengal basin and the Arabian Sea basins. Of the above 2 sources Bay of Bengal generate most cyclones. The reason behind that is,
- Bay of Bengal has higher surface temperature in comparison and tropical cyclones need a higher temperature for cyclone genesis.
- Cyclones of low intensity also come from the foreign sources. Neighboring Pacific Ocean seas are more prone to cyclones. Typhoons originating in near Philippines, China, Thailand and Malaysia enter the Andaman Sea of Bay of Bengal after they weaken in their native regions.
- Coastal region of east is of low topography in comparison to Western areas with Ghats of high elevation.
- Most of the cyclones in the Arabian Sea are local. They collapse a little after making landfall as there is no back-up supply.
Naming of Cyclones The World Meteorological Organisation/Economic and Social Commission for Asia and the Pacific Panel on Tropical Cyclones, at its twenty-seventh session held in 2000 in Muscat, Oman, agreed to assign names to the tropical cyclones in the Bay of Bengal and Arabian Sea. Commencement of Naming of tropical cyclones over north Indian Ocean was done from September 2004. For tropical cyclones developing in the North Indian Ocean, countries like India, Sri Lanka, Bangladesh, Maldives, Myanmar, Oman, Pakistan and Thailand send their names to the regional tropical cyclone committee. At present, all eight countries have submitted eight names each for naming future cyclones. The name Fani was chosen from this list containing 64 names. Of the 64 names suggested by these eight countries, 57 have been utilized.
- The main purpose of naming a tropical cyclone is basically for people to easily understand and remember the tropical cyclone in a region, thus to facilitate tropical cyclone disaster risk awareness, preparedness, management and reduction.
- Another important reason why cyclones are named is to help authorities quickly identify storms and keep a track of them.
- Naming cyclones also helps media in reporting warning related to the approaching cyclone.
Vulnerability to Cyclones in India
- Approximately 5700 km out of around 7516 kms of India’s coastline, its flat coastal terrain and high population density are extremely vulnerable to cyclones and its associated hazards such as storm surges, high winds and heavy rainfall.
- Approximately 40 percent of the total population in the maritime States lives within 100 kms of coastlines.
- Recurrent cyclones account for a large number of deaths, loss of livelihood opportunities, loss of public and private property, and severe damage to infrastructure. This reverses developmental gains at regular intervals.
Cyclone Risk Mitigation 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.
National Cyclone Risk Mitigation Project Phase-II For the NCRMP Phase-II, the Central Government will provide financial assistance equivalent to Rs. 1881.20 crore through a World Bank loan. The remaining amount of Rs. 480.15 crore will be provided by the State Governments of Goa, Gujarat, Karnataka, Kerala, Maharashtra and West Bengal. The broad objectives of the project are to
- provide cyclone forecasting, tracking and warning systems,
- Cyclone risk mitigation and capacity building in multi-hazard risk management.
Major infrastructure which will be constructed under the project includes multipurpose cyclone shelters, access roads, saline embankments and underground cabling. The primary focus of the project is disaster mitigation with an objective to minimize loss of lives and property in the vulnerable States. Cyclone warning system in India The present organisational structure for cyclone warnings is a three-tier one, with
- The (Area Cyclone Warning Centers, Cyclone warning centers) ACWCs/CWCs actually performing the operational work of issuing the bulletins and warnings to the various user interests,
- While the cyclone warnings (Directorate) New Delhi and the Deputy Director General of Meteorology (Weather Forecasting), through Weather Central, Pune coordinates and guides the work of the ACWCs/CWCs, exercises supervision over their work and takes necessary measures for continued improvement and efficiency of the storm warnings system of the country as a whole.
- The ultimate responsibility for operational storm warning work for the respective areas however, rests with the ACWCs and CWCs.
At present there are 12 conventional early cyclone warning radars installed on the coasts. Cyclone warnings are provided by the IMD from the Area Cyclone Warning Centres (ACWCs) at Kolkata, Chennai and Mumbai and Cyclone Warning Centres (CWCs) at Vishakhapatnam, Bhubaneswar and Ahmedabad.
Issues identified in present warning system