Author: Nitesh Gughane

Context

Recently Cyclone Tauktae and Cyclone Yaas wreaked havoc in several states of India with  the credit for the cyclogenesis can be given to exceptionally warmer Indian seas this year, making atmospheric and ocean conditions favourable for frequent formation of cyclones and their rapid intensification.

Introduction

• Cyclones are rapid inward air circulation around a low-pressure area. The air circulates in an anticlockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere.
• Cyclones are usually accompanied by violent storms and bad weather.
• The word Cyclone is derived from the Greek word Cyclos meaning the coils of a snake. It was coined by Henry Peddington because the tropical storms in the Bay of Bengal and the Arabian Sea appear like coiled serpents of the sea.

What are tropical Cyclones?

• A Tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
• Cyclones are formed over slightly warm ocean waters. The temperature of the top layer of the sea, up to a depth of about 60 meters, need to be at least 28°C to support the formation of a cyclone.
• This explains why the April-May and October-December periods are conducive for cyclones.
• Then, the low level of air above the waters needs to have an ‘anticlockwise’ rotation (in the northern hemisphere; clockwise in the southern hemisphere).
• During these periods, there is an ITCZ in the Bay of Bengal whose southern boundary experiences winds from west to east, while the northern boundary has winds flowing east to west.
• Once formed, cyclones in this area usually move northwest. As it travels over the sea, the cyclone gathers more moist air from the warm sea which adds to its heft.

Formation of a Cyclone

(The above figure shows how cyclones form. The green arrows show where warm air is rising. The red arrows indicate where cool air is sinking)

Requirements for a Cyclone to form

There are six main requirements for tropical cyclogenesis:

• Sufficiently warm sea surface temperatures.
• Atmospheric instability.
• High humidity in the lower to middle levels of the troposphere.
• Enough Coriolis force to develop a low-pressure center.
• A preexisting low-level focus or disturbance.
• Low vertical wind shear.

Origin

• The formation and initial development of a cyclonic storm depends upon the transfer of water vapour and heat from the warm ocean to the overlying air, primarily by evaporation from the sea surface.
• It encourages formation of massive vertical cumulus clouds due to convection with condensation of rising air above the ocean surface.
• Under favorable conditions, multiple thunderstorms originate over the oceans. These thunderstorms merge and create an intense low pressure system (wind is warm and lighter).

Early Stage 

• In the thunderstorm, air is uplifted as it is warm and light. At certain height, due to lapse rate and adiabatic lapse rate, the temperature of air falls and moisture in the air undergoes condensation.
• Condensation releases latent heat of condensation making the air more warmer. It becomes much lighter and is further uplifted.
• The space is filled by fresh moisture laden air. Condensation occurs in this air and the cycle is repeated as long as the moisture is supplied.
• Due to excess moisture over oceans, the thunderstorm intensifies and sucks in air at much faster rate. The air from surroundings rushes in and undergoes deflection due to Coriolis force creating a cyclonic vortex (spiraling air column. Similar to tornado).
• Due to centripetal acceleration (centripetal force pulling towards the center is countered by an opposing force called centrifugal force), the air in the vortex is forced to form a region of calmness called an eye at the center of the cyclone. The inner surface of the vortex forms the eye wall, the most violent region of the cyclone.
• All the wind that is carried upwards loses its moisture and becomes cold and dense. It descends to the surface through the cylindrical eye region and at the edges of the cyclone.
• Continuous supply of moisture from the sea is the major driving force behind every cyclone. On reaching the land the moisture supply is cut off and the storm dissipates.
• If ocean can supply more moisture, the storm will reach a mature stage.

Mature Stage

• At this stage, the spiraling winds create multiple convective cells with successive calm and violent regions.
• The regions with cumulonimbus cloud (rising limbs of convective cell) formation are called rain bands below which intense rainfall occurs.
• The ascending air will lose moisture at some point and descends (subsides) back to surface through the calm regions (descending limbs of convection cell – subsiding air) that exist between two rain bands.
• Cloud formation is dense at the center. The cloud size decreases from center to periphery.
• Rain bands are mostly made up of cumulonimbus clouds. The ones at the periphery are made up of nimbostratus and cumulus clouds.
• The dense overcast at the upper levels of troposphere is due to cirrus clouds which are mostly made up of hexagonal ice crystals.
• The dry air flowing along the central dense overcast descends at the periphery and the eye region.

Destruction Caused by Cyclones

Cyclones are disastrous in many ways. They do more harm than any good to the coastal areas.

1) Strong Winds

• 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.

2) 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.
• Heavy rainfall from a cyclone is usually spread over a wide area and cause large scale soil erosion and weakening of embankments.

3) 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 seawater inundates low lying areas of coastal regions drowning human beings and life stock.
• It causes eroding beaches and embankments, destroys vegetation and leads to the reduction of soil fertility.

Recent Cyclones

Cyclone Tauktae

• Extremely Severe Cyclonic Storm Tauktae was a powerful tropical cyclone in the Arabian Sea that became the strongest tropical cyclone to make landfall in the Indian state of Gujarat since the 1998 Gujarat cyclone and one of the strongest tropical cyclones to ever affect the west coast of India.
• Tauktae brought heavy rainfall and flash floods to areas along the coast of Kerala and on Lakshadweep. There were reports of heavy rain in the states of Goa, Karnataka and Maharashtra as well.
• Tauktae resulted in at least 169 deaths in India, and left another 81 people missing.
• 66 people died, at least 20 people are still missing after Barge P305 sank near Heera oil field, off the coast of Mumbai, although the Indian Navy said it had rescued 186 survivors of the 270 people aboard by May 19.
• Losses from Tauktae are estimated at ₹15,000 crore or US$2.1 billion.

Cyclone Yaas

• Very Severe Cyclonic Storm Yaas was a relatively strong and highly damaging tropical cyclone that made landfall in Odisha and brought significant impacts to West Bengal during late May 2021.
• Yaas formed from a tropical disturbance that the Indian Meteorological Department first monitored on May 23.
•  Evacuations were also ordered, starting on May 24 on low-lying areas in East Midnapore and West Midnapore and Jhargram. 
• As of May 28, 20 people have been reported dead due to Yaas.
• The total damages in West Bengal, the most heavily impacted state from Yaas, were estimated to be around ₹20 thousand crore (US$2.76 billion).

Management of Cyclones in India

• In 2005, the country introduced new laws to set up what’s called the National Disaster Management Authority, a central agency charged with one thing: responding to and minimizing the impact of disasters.

A year later, in 2006, India established a National Disaster Response Force (NDRF), a specialized corps of highly trained men and women focused on disasters such as cyclones and earthquakes. It’s now comprised of almost 25,000 personnel.

Apart from institutional measures, there are many structural and non-structural measures that have been taken 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.

Issues in Cyclone Mitigation

• Post than pre focus: Disaster management in India is largely confined to post-disaster relief works. It is more about management than loss prevention.
• Population: One-third of the population in India lives in the coastal area. Most of them are marginalized people who are ill-prepared and unable to cope up with a disaster.
• Poor response: The warning of a cyclone is not properly communicated between the concerned agencies. In many cases, the warning is not taken seriously by the agencies which cause delayed effort for the prevention of a disaster. This was evident in the recent Ockhi cyclone disaster.
• Lack of awareness: among people about the impact and magnitude of the disaster. Also what to act during and post disasters.
• Coordination Issues: There is also a lack of coordination between the local communities for search and rescue missions. Also poor coordination state and center coordination and its agencies.

Measures need to be taken for effective mitigation

Pre Disaster

• Provide cyclone forecasting, tracking and warning systems
• Construction of cyclone shelters, cyclone-resistant buildings, road links, bridges, canals, drains etc.
• Establishing Early Warning Dissemination System (EWDS) and Capacity building for coastal communities.

During disaster

• Cautionary advice should be put out on social platforms urging people to stay safe
• The perception of people decides the intensity of the disaster. If people take necessary proactive steps to deal with disaster then even the severe disaster can be dealt with minimum damage.
• Delivery of food and health care via mobile hospitals, with priorities to women child & elders.
• Protection of the community and their evacuation and quicker response.

Post-disaster

• It is vital that the learning from each event is shared nationally, and the capacity of officials and communities to manage disasters built continuously.
• Among the securities available to individuals in many countries is insurance against property losses. Viable policies should be made available in India too.
• Providing alternative means of communication, energy and transport just after the disaster.

Way Forward

• Infrastructure of the regions that are vulnerable to cyclonic activities must be made/ designed so that evacuation process gets easy and damage gets minimized.
• Forecast techniques must be improved so as to get more time for preparing before a cyclonic storm.
• School and social awareness campaigns must be organized in the vulnerable areas for better individual preparedness.
• NDRF and other emergency forces must be made more equipped with emergency kits and modern machinery for them to play a better role in keeping them and others safe.
• Now the imperative for India is not only to have infrastructure that is resilient, functional and that can bounce back after a disaster, but also to have infrastructure withstand and be operational during a crisis.
• For this India need to employ more technology, strict following of command structure, and most importantly the participation and cooperation of local communities in the affected area.
• There must be test facilities made for the emergency forces to prepare themselves better for the actual situations.