Cyclones can have a devastating impact on India, causing damage to infrastructure, loss of life, and environmental harm:

Cyclones can have a devastating impact on India, causing damage to infrastructure, loss of life, and environmental harm: 

Infrastructure damage: Cyclones can damage or destroy buildings, roads, bridges, power and communication towers, and hospitals. 

India experiences an average of 2 to 4 tropical cyclones each year, with most of them affecting the east coast. The west coast is less prone to cyclones, but when they do occur, they usually hit the states of Gujarat, Maharashtra, Goa, Karnataka, and Kerala. 

Flooding: Cyclones can cause torrential rainfall that leads to flooding, which can damage houses and buildings. Storm surges can also cause flooding by raising sea levels and inundating low-lying coastal areas. 

Erosion: Storm surges can erode beaches and embankments. 

Loss of life: Cyclones can cause a large number of deaths. For example, the 1977 cyclone in Andhra Pradesh killed 10,000 people. 

Loss of livelihood: Cyclones can lead to loss of livelihood opportunities. 

Environmental harm: Cyclones can damage vegetation and livestock, and make soil infertile. 

Coral reef damage: Cyclones can cause severe bleaching of coral reefs, which can lay bare stretches of reefs.

Everything about Cyclones: Formation, Causes and Impact

how are cyclones formed

Information collected by satellites suggests that cyclones generally form in low-pressure zones and over warm intertropical waters. These are gigantic and deadly storms that create havoc and severe damages to life and property.

According to the World Meteorological Organisation approximately 85 tropical storms develop over the warm tropical latitude oceans.

Read on to find everything about the types, causes, occurrence, impact, hazard zones and preventive measures of cyclones in this article.

What Are Cyclones?

In meteorological terms, a cyclone is a wind system that rotates inwards (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere) around a strong low-pressure centre.

Generally, when winds rise above 118 kmph, it is known as a cyclone. These rotating winds forming over the Indian ocean and south of the Pacific Ocean are termed as cyclones. In other regions they are usually called by different names such as, typhoons, hurricanes etc.

To understand the severity of cyclones, one must learn in detail about its process of formation and its categories.

How Are Cyclones Formed?

Scroll down to the following section to understand the formation of a cyclone -

Warm and moist air over the ocean rises upward due to less density, leaving less air near the ocean surface,As a result, it starts to create a low-pressure zone.

Due to the surrounding high-pressure areas, air flows into this low-pressure and eventually warms up, forming a cycle.

With the constant heating rising of the warm air and evaporation process, the entire cloud and wind system starts to spin and grow.

With acquiring more speed, the eye of the cyclone starts to form in the centre. This central zone signifies the lowest air pressure area and is calm and clear. Further, the high-pressure air from above flows towards this region.

When the wind’s rotating speed reaches 63 kmph, it is called a tropical storm. However, when wind speed reaches 119 kmph, tropical cyclone formation takes place.

Now that you know the process of formation of a cyclone, let's take a look at the categories of a cyclone.

What Are the Different Categories of Cyclones?

The categories of a cyclone depends on its wind strength. From the following table, you will be able to estimate the damage a cyclone can cause after its landfall, depending on its wind speed.

Category

Wind Speed (in kmph)

Damage at Landfall

1

119-153

Minimal

2

154-177

Moderate

3

178-210

Extensive

4

211-250

Extreme

5 More than 250C catastrophic

Now, let's find out the causes behind the formation of a cyclone.

What Are the Causes of a Cyclone?

After knowing the answer to your question, "how are cyclones formed?" you might also like to know about why a cyclone occurs or what causes it.

Here are the factors responsible for cyclone formation -

Warm temperature at sea surfaces.

Coriolis force impacts the area that forms a low-pressure zone.

Atmospheric instability.

Increased humidity in the lower to middle levels of the troposphere.

Low vertical wind shear.

Pre-existing low-level disturbance or focus.

Now that you know how cyclones are formed and what causes them, let's look at the types of cyclones that have occurred in India over the years.

Cyclones that Occurred in India Till Now

With respect to the above table, the following list of cyclones have occurred in India over the past few years -

Name of the Cyclone

Type of the Cyclone

Yaas

Severe cyclonic storm over the Bay of Bengal.

Tauktae

Very severe cyclonic storm originating from the Arabian Sea.

Nisarga

Severe cyclonic storm emerging from the Arabian Sea.

Amphan

Super cyclonic storm formed in the Bay of Bengal.

Kyarr

Super cyclonic storm emerging from the Arabian Sea.

Maha

Extremely severe cyclonic storm originating in the Arabian Sea.

Vayu

Severe cyclonic storms originate from the Arabian Sea.

Hikka

Very severe cyclonic storm emerging from the Arabian Sea.

Fani

Extremely severe cyclonic storm originating from the Indian Ocean.

BOB 03

Severe cyclonic storm formed in the central Bay of Bengal

Bulbul

A very severe cyclonic storm emerged from the Bay of Bengal.

Now let’s delve into the impact of cyclones.

Impact of Cyclones in India

If you know how a cyclone is formed, you must know that it is often accompanied by strong winds, torrential rains and storm surge. These three elements causes impact to a great extent in the following ways -

Strong winds cause damages to infrastructure, uproots trees, and lead to other catastrophes.

Torrential rainfall leads to unprecedented floods and damages to houses and buildings.

Due to storm surge, seawater levels rise, and the coastal areas are exposed to flooding.

The rise in seawater level also erodes beaches and embankments.

Severe cyclonic storms resulting in floods can damage vegetation and livestock.

Due to the strong winds and conditions, the soil tends to become infertile.

In addition to this, cyclonic storms result in the loss of human, plant and animal lives and affect the country's economy.

Next up, let's look at the cyclone-prone zones in India.

Cyclone Hazard Zones in India

As per the Indian Meteorological Department, 13 coastal states and Union Territories in India are prone to a cyclone. The eastern coast of India is more prone to cyclonic conditions than the western coast. However, because of the long coastline of India of 7516.6 km both the coasts of India experience cyclonic storms quite frequently.

Among both the coasts, some states are more vulnerable to cyclones than the others. The most vulnerable states in India that are majorly prone to cyclonic impact are as follows -

West Bengal

Andhra Pradesh

Tamil Nadu

Odisha

Puducherry (UT)

Gujarat

People residing in and around the above areas must equip themselves with certain preventive measures to carry out any damage control.

Preventive Measures to Combat Cyclones in India

The National Disaster Management Authority (NDMA) advises individuals to take the following steps to stay safe during cyclones -

It is necessary to stay indoors during a cyclonic storm and keep away from electrical mains.

In extreme situations, one must prepare an emergency kit that is essential for survival.

It is also vital to keep tabs on regular weather forecast updates and rely on official warnings.

In case your house is unsafe, it is advisable to shift before the onset of a cyclone.

Further, in collaboration with the NDMA, the Government carries out proper evacuation measures for fishermen and the coastal dwellers before the cyclone makes landfall.

With a detailed knowledge of how cyclones are formed and their causes, one can take sufficient precautions and avoid the harsh consequences.

Cyclone

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. The air circulates inward in an anticlockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere. Cyclones are classified as: (i) extra tropical cyclones (also called temperate cyclones); and (ii) tropical cyclones. 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.

Classifications

Cyclones are classified as extra tropical cyclones (also called temperate cyclones); and tropical cyclones.

The World Meteorological Organisation (WMO, 1976) uses the term 'Tropical Cyclone’ to cover weather systems in which winds exceed ‘Gale Force’ (minimum of 34 knots or 63 kph). Tropical cyclones are the progeny of ocean and atmosphere, powered by the heat from the sea; and driven by easterly trades and temperate westerlies, high planetary winds and their own fierce energy.

In India, cyclones are classified by:

Strength of associated winds,

Storm surges

Exceptional rainfall occurrences.

Extra tropical cyclones occur in temperate zones and high latitude regions, though they are known to originate in the Polar Regions.

Cyclones that developin the regions between the Tropics of Capricorn and Cancer are called tropical cyclones. Tropical cyclones are large-scale weather systems developing over tropical or subtropical waters, where they get organized into surface wind circulation.

Worldwide terminology

Cyclones are given many names in different regions of the world – They are known as typhoons in the China Sea and Pacific Ocean; hurricanes in the West Indian islands in the Caribbean Sea and Atlantic Ocean; tornados in the Guinea lands of West Africa and southern USA.; willy-willies in north-western Australia and tropical cyclones in the Indian Ocean. 

Indian Meteorological Department

The criteria below has been formulated by the Indian Meteorological Department (IMD), which classifies the low pressure systems in the Bay of Bengal and the Arabian Sea on the basis of capacity to damage, which is adopted by the WMO.

Type of Disturbances Wind Speed in Km/h Wind Speed in Knots

Low Pressure Less than 31 Less than 17

Depression 31-49 17-27

Deep Depression 49-61 27-33

Cyclonic Storm 61-88 33-47

Severe Cyclonic Storm 88-117 47-63

Super Cyclone More than 221 More than 120

1 knot - 1.85 km per hour

Cyclones are classified into five different levels on the basis of wind speed. They are further divided into the following categories according to their capacity to cause damage:-

Cyclone Category Wind Speed in Km/h Damage Capacity

01 120-150 Minimal

02 150-180 Moderate

03 180-210 Extensive

04 210-250 Extreme

05 250 and above Catastrophic

Storm surges (tidal waves) are defined as the rise in sea level above the normally predicted astronomical tide. Major factors include:

A fall in the atmospheric pressure over the sea surface

Effect of the wind

Influence of the sea bed

A funnelling effect

The angle and speed at which the storm approaches the coast

The tides

The very high specific humidity condenses into exceptionally large raindrops and giant cumulus clouds, resulting in high precipitation rates. When a cyclone makes landfall, rain rapidly saturates the catchment areas and the rapid runoff may extensively flood the usual water sources or create new ones.

How Cyclones are formed

The development cycle of tropical cyclones may be divided into three stages:

Formation and Initial Development Stage

The formation and initial development of a cyclonic storm depends upon various conditions. These are:

A warm sea (a temperature in excess of 26 degrees Celsius to a depth of 60 m) with abundant and turbulent transfer of water vapour to the overlying atmosphere by evaporation.

Atmospheric instability encouraging formation of massive vertical cumulus clouds due to convection with condensation of rising air above ocean surface.

Mature Tropical Cyclones

When a tropical storm intensifies, the air rises in vigorous thunderstorms and tends to spread out horizontally at the tropopause level. Once air spreads out, a positive perturbation pressure at high levels is produced, which accelerates the downward motion of air due to convection. With the inducement of subsidence, air warms up by compression and a warm ‘Eye’ is generated. Generally, the ‘Eye’ of the storms has three basic shapes: (i) circular; (ii) concentric; and (iii) elliptical. The main physical feature of a mature tropical cyclone in the Indian Ocean is a concentric pattern of highly turbulent giant cumulus thundercloud bands.

Modification and Decay

A tropical cyclone begins to weaken in terms of its central low pressure, internal warmth and extremely high speeds, as soon as its source of warm moist air begins to ebb, or is abruptly cut off. This happens after its landfall or when it passes over cold waters. The weakening of a cyclone does not mean that the danger to life and property is over.

Indian Context

The Indian subcontinent is one of the worst affected regions in the world. The subcontinent with a long coastline of 8041 kilometres is exposed to nearly 10 per cent of the world’s tropical cyclones. Of these, the majority of them have their initial genesis over the Bay of Bengal and strike the East coast of India. On an average, five to six tropical cyclones form every year, of which two or three could be severe. More cyclones occur in the Bay of Bengal than the Arabian Sea and the ratio is approximately 4:1. Cyclones occur frequently on both the coasts (the West coast - Arabian Sea; and the East coast - Bay of Bengal). An analysis of the frequency of cyclones on the East and West coasts of India between 1891 and 1990 shows that nearly 262 cyclones occurred (92 of these severe) in a 50 km wide strip above the East coast. Less severe cyclonic activity has been noticed on the West coast, where 33 cyclones occurred the same period, out of which 19 of were severe.

Tropical cyclones occur in the months of May-June and October-November. Cyclones of severe intensity and frequency in the North Indian Ocean are bi-modal in character, with their primary peak in November and secondary peak in May. The disaster potential is particularly high during landfall in the North Indian Ocean (Bay of Bengal and the Arabian Sea) due to the accompanying destructive wind, storm surges and torrential rainfall. Of these, storm surges cause the most damage as sea water inundates low lying areas of coastal regions and causes heavy floods, erodes beaches and embankments, destroys vegetation and reduces soil fertility.

Cyclones vary in diameter from 50 to 320 km but their effects dominate thousands of square kilometers of ocean surface and the lower atmosphere. The perimeter may measure 1,000 km but the powerhouse is located within the 100-km radius. Nearer the Eye, winds may hit at a speed of 320 km. Thus, tropical cyclones, characterized by destructive winds, torrential rainfall and storm surges disrupt normal life with the accompanying phenomena of floods due to the exceptional level of rainfall and storm surge inundation into inland areas. Cyclones are characterized by their devastating potential to damage structures, viz. houses; lifeline infrastructure-power and communication towers; hospitals; food storage facilities; roads, bridges and culverts; cropss etc. The most fatalities come from storm surges and the torrential rain flooding the lowland areas of coastal territories.

zone

 

Recover and build

After ‘All Clear’ is issued for back movement by ‘State’ give attention to the following:

Whether ‘roads’ for reaching home is recommended by authorities

Whether power lines are safe

Whether transport arrangement is approved by authorities

Pure drinking water is available

Sewage lines are working

Any epidemic spread in the area

Safety of neighbor(s) assured

Emergency Kit

Battery operated torch

Extra batteries

Battery operated radio

First aid kit and essential medicines

Important papers (Ration card, Voter ID card, Aadhar card etc)

Emergency food (dry items) and water (packed and sealed)

Candles and matches in a waterproof container

Knife

Chlorine tablets or powdered water purifiers

Cash, Aadhar Card and Ration Card

Thick ropes and cords

Shoes