GS 1 – Important Geophysical Phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.
GS 3 – Disaster and Disaster Management.
Source : The Hindustan Times dated 16/05/2021 https://www.hindustantimes.com/editorials/the-climate-crisis-and-cyclones-101621167547861.html
Context : A severe cyclonic storm, Tauktae , intensified into a “very severe cyclonic storm” over the east central Arabian Sea, and affected the Kerala, Goa, Karnataka, Maharashtra and Gujarat coastlines over the last week.
In recent years, strong cyclones have been developing in the Arabian Sea more frequently than earlier.
A cyclone is any low-pressure area with winds spiralling inwards.
- Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction due to violent winds (squalls), very heavy rainfall (torrential rainfall) and storm surge.
- They are irregular wind movements involving closed circulation of air around a low pressure center. This closed air circulation (whirling motion) is a result of rapid upward movement of hot air which is subjected to Coriolis force.
Conditions necessary for a tropical cyclone formation
- Large sea surface with temperature higher than 27° C,
- Presence of the Coriolis force enough to create a cyclonic vortex,
- Small variations in the vertical wind speed,
- A pre-existing weak low-pressure area or low-level-cyclonic circulation,
- Upper divergence above the sea level system.
- It is an apparent force that, as a result of the earth’s rotation deflects moving objects (such as projectiles or air currents) to the right in the northern hemisphere and to the left in the southern hemisphere.
- The Coriolis force is zero at the equator (no cyclones at equator because of zero Coriolis Force) but it increases with latitude. Coriolis force at 5° latitude is significant enough to create a storm [cyclonic vortex].
- About 65 per cent of cyclonic activity occurs between 10° and 20° latitude.
Formation of tropical cyclones
- Under favorable conditions, multiple thunderstorms originate over the oceans. These thunderstorms merge and create an intense low pressure system (wind is warm and lighter).
- 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.
- The “eye” is a roughly circular area of comparatively light winds and fair weather found at the center of a severe tropical cyclone.
- There is little or no precipitation and sometimes blue sky or stars can be seen.
Categories of tropical cyclones
Naming of tropical cyclones
- According to WMO (World Meteorological Organization) guidelines, countries in every region are supposed to give names for cyclones.
- The North Indian Ocean Region covers tropical cyclones formed over Bay of Bengal and Arabian Sea.
- India Meteorological Department (IMD), one of the six Regional Specialised Meteorological Centres (RSMC) in the world, is mandated to issue advisories and name tropical cyclones in the north Indian Ocean Region.
- Cyclone Tauktae is a tropical cyclone, named by Myanmar.
- Normally,there are fewer cyclones over Arabian Sea compared to Bay of Bengal because :
- High frequency of typhoons over Northwest Pacific( about 35 % of global average)
- Also majority of Cyclones over the Bay of Bengal weaken over land after landfall,and hence the frequency of migration into Arabian Sea is low.
- In addition to all the above the Arabian Sea is relatively cooler.(In Bay of Bengal, the sea surface temperature remains consistently above 28 degree Celsius, while the Arabian Sea area remained a degree or two cooler.)
- But recently climate scientists have warned that the Arabian Sea is fast becoming a “cyclone hotbed”
- Annually, five cyclones on average form in the Bay of Bengal and the Arabian Sea combined. Of these, four develop in the Bay of Bengal and one in the Arabian Sea. (4:1 ratio)
- In 2019 the Arabian Sea witnessed an abnormally high number of cyclones – 5. The last time so many cyclones formed over the Arabian Sea was in the year 1902. (while Bay of Bengal witnessed only 3 cyclones.)
- Tauktae is the fourth cyclone in consecutive years to have developed in the Arabian Sea, that too in the pre-monsoon period (April to June). All these cyclones since 2018 have been categorised either ‘Severe Cyclone’ or above.
The reason for increased frequency of cyclones in Arabian sea could be:
- Sea Surface Temperatures are often above the “warm pool threshold”, which supports the formation of intense cyclones.
- Eg: Currently, sea water up to depths of 50 metres has been very warm, supplying ample energy to enable the intensification of Cyclone Tauktae.- the more the heat released through condensation of water vapour, the steeper the drop in pressure.
- The Intergovernmental Panel on Climate Change (IPCC) report, Ocean and Cryosphere in a Changing Climate says that climate change and the global warming associated with it has led to an increase in the occurrence of ESCSs(extremely severe cyclonic storms) in the Arabian Sea.
An analysis of extreme weather events in the past 50 years has revealed that though tropical cyclones were the least frequent event, they caused 28.6% of the mortalities, second only to floods responsible for maximum human deaths.
Management of cyclones in India
NDMA guidelines for the Management of Cyclones
- Non – Structural Measures
- Early Warning Systems:
- Eg: Automatic Weather Stations, Doppler radars, High Wind Speed Recorders, Ocean buoys, Unmanned Aerial Vehicles etc.
- -provide critical information for tracking and forecasting intensity of cyclones.
- Communication and Dissemination Systems:
- Eg : Cellular telephone network, Disaster Warning System (DWS) terminals, etc.
- A holistic approach to Coastal Zone Management (CZM)
- Mangrove forests and shelterbelts constitute Bio-shields in coastal areas and provide ecological security. Their preservation is to be done by effective implementation of Coastal Regulation Zone (CRZ) Rules.
- Awareness Generation.
- Early Warning Systems:
- Structural Measures
- Ensure availability of adequate numbers of shelters, community centres/school buildings, places of worship, etc., which can be utilised for moving people from vulnerable areas to safety.
- To provide at least one all-weather link road for each village that is accessible during cyclone or flooding periods.
- Construction of ‘saline embankments’ – to protect habitation, agriculture crop and important installations along the coast.
National Cyclone Risk Mitigation Project (NCRMP):
- Government has drawn up NCRMP to be implemented with World Bank assistance of $300 million.
- Objective – to strengthen the structural and non-structural cyclone mitigation efforts and reduce the risk and vulnerability of the coastal districts which are prone to cyclones.
- NCRMP consists of the following four components
- Component A: Improvement of early warning dissemination system of cyclone warnings.
- Component B: Cyclone risk mitigation investment Eg :construction of cyclone shelters.
- Component C: Technical assistance for hazard risk management and capacity building.
- Component D: Project management and institutional support.
Phase II of the NCRMP was approved in 2015 and was to be completed in 2020 for Goa, Gujarat, Karnataka, and Maharashtra. But data shows that early warning systems and multi-purpose cyclone shelters are yet to be completed in many of these states.
Disaster Risk Management and Capacity Development
- Establishment of a comprehensive Cyclone Disaster Management Information System covering all phases of disaster management to provide online services to the states.
- Community Based Disaster Management (CBDM) to build the capacity of communities to assess their vulnerability to both human induced and natural hazards and develop strategies and resources necessary to prevent and/or mitigate the impact.
About 8% of our Country’s area and one-third of its population live in 13 coastal states and UTs who are vulnerable to cyclone related disasters. With the global warming continuing unabated, there is the additional risk of increased frequency and intensity of cyclones and other extreme weather events .
Hence moving forward, the only option to limit cyclone-related casualties is to understand climate science, warnings, and be cyclone-ready.