Why Arabian Sea is transforming into a New Cyclonic Hotbed? – Explained, Pointwise

Introduction

The Arabian Sea used to be cyclone shy! But it is changing now, and changing fast!

Cyclones are among the most devastating extreme weather events that India faces every year. The strong winds and heavy rains that accompany cyclones cause immense loss of life and property along the coastline of India.  Approximately 1.4 lakh people died by cyclones, floods, and other weather extremes during the past five decades.

The recent formation of Cyclone Tauktae makes 2021 the fourth consecutive year to witness an Arabian Sea cyclone during the pre-monsoon season (April–June). The changing climate and rising global warming have converted the Arabian Sea into a new hotbed for cyclonic activities. Earlier the majority of the cyclones used to occur in the Bay of Bengal.

Current Scenario
  • Cyclone Tauktae developed over the Arabian Sea on May 14, 2021, and got converted into a very severe cyclonic storm (VSCS) on May 16, 2021. It is expected to hit southern Gujarat on May 18, 2021. 
  • In recent years, strong cyclones have been developing on the Arabian Sea more frequently than earlier.
About Tropical Cyclones
  • They are violent storms that originate over oceans in tropical areas.
  • They create a whirl in the atmosphere with very strong winds circulating around it. The direction is anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
  • The pressure gradient falls towards the center from all directions and therefore winds try to converge towards the center from all directions.
  • They develop in the North Indian Ocean region (Bay of Bengal and Arabian Sea) during the pre-monsoon and post-monsoon (October to December) periods. May-June and October-November are known to produce cyclones of severe intensity that affect the Indian coasts.
  • It is anticipated that around 76 per cent of India’s coastline is susceptible to cyclones and tsunamis.
  • Conditions for Formation of Tropical Cyclones:
    • A consistent source of heat as tropical cyclones are thermally induced low-pressure systems.
    • Large sea surface with a temperature higher than 27° C which is possible only during the late summers i.e. September, October, and November
    • Presence of the Coriolis force. It is the result of the earth’s rotation and deflects objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
    • 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.
Past Trend of Cyclonic Activities
  • The Arabian Sea has been comparatively less prone to cyclonic storms than the Bay of Bengal. In the usual course, there was an occurrence of one extremely severe cyclone every four-five years in the Arabian Sea.
  • During the period 1891-2000, nearly 308 tropical cyclones crossed the east coast, of which 103 were severe in intensity. Similarly, 48 cyclones crossed the west coast of which 24 were severe. 
 Reasons behind past trends
  • First, high sea surface temperatures along with high humidity in the Bay of Bengal triggers extremely strong cyclones.
  • Second, sluggish winds along with warm air currents in the Bay of Bengal keep temperatures relatively high.
  • Third, the constant inflow of freshwater from the Ganga and Brahmaputra rivers makes it impossible for the warm water to mix with the cooler water below.
  • Fourth, cyclonic winds easily move into the Bay of Bengal due to the presence of moisture sources from rivers and the absence of any large landmass.
  • Fifth, the Arabian Sea receives stronger winds that help dissipate the heat, and the lack of constant freshwater supply helps the warm water mix with the cool water thereby reducing the temperature. 
    • Almost 50% of the storms don’t sustain as the west-central and the north Arabian Sea have a colder sea temperature than other adjacent regions. 

However, this trend is changing, with a greater number of cyclones being developed in the Arabian Sea.

Reasons behind increasing cyclonic activities in the Arabian Sea
  • Annually, five cyclones on average used to form in the Bay of Bengal and the Arabian Sea combined. Among these, four develop in the Bay of Bengal and one in the Arabian Sea.
  • Previously, tropical cyclones in the Arabian Sea were restricted to Gujarat. However, now even Kerala and Karnataka have also become more vulnerable to cyclones. A recent example is ‘Ockhi’.
  • Tauktae is the fourth cyclone in consecutive years to have developed in the Arabian Sea. Cyclone Mekanu hit Oman in 2018, Cyclone Vāyu struck Gujarat in 2019 and Cyclone Nisarga hit Maharashtra in 2020.
  • Apart from frequency, a rise in the intensification rate is also observed. All these cyclones since 2018 have been categorised either ‘Severe Cyclone’ or above.
    • Tauktae took only 2 days to become VSCS while Cyclone Mekanu and Cyclone Nisarga had developed slower, taking 4 and 5 days respectively.  
Reasons behind changing trends
  • First, sea surface temperatures in the Arabian Sea have increased rapidly during the past century due to global warming. Temp. now is 1.2–1.4 °C higher than the temperature witnessed four decades ago. These warmer temperatures support active convection, heavy rainfall, and intense cyclones.
  • Second, the rising temperature is also enabling the Arabian Sea to supply ample energy for the intensification of cyclones. Currently, seawater up to depths of 50 metres has been very warm that allowed Cyclone tauktae to become a VSCS in only 2 days.
  • Third, the Arabian Sea is also providing conducive wind shear for cyclones. For instance, a higher level easterly wind drove the depression of Cyclone Ockhi from the Bay of Bengal to the Arabian Sea.
  • Fourth, greater occurrence of El Niño Modoki. It is a climate phenomenon that means ‘pseudo El Niño’ and creates conditions that are not conducive for cyclogenesis in the Bay of Bengal. However, this condition is conducive for the formation of cyclones in the Arabian Sea.
    • El Nino is associated with suppressing cyclone formation in the Arabian Sea.
Concerns associated with changing trends
  • Covid management: There is a concern about the impact of the cyclonic storm on the battle against Covid-19. The rain and flooding may set back social distancing and other necessary measures at evacuation centres and relief camps.
  • Delay in Monsoon: The cyclone Tauktae is expected to interfere with the normal progression of the Indian Monsoon by sucking all the moisture from the monsoon winds towards itself.  The strong low-pressure areas at their core induce the surrounding winds to rush towards them.
  • Rise in Extreme Rainfall events: Widespread extreme rainfall events that cause floods have also increased by threefold over India, in response to Arabian Sea warming. This has deeply impacted the lives, livelihood, infrastructure and ecology of the region.
  • Forecasting Challenge: The new trend is encouraging more and more rapid intensification of cyclones. State-of-the-art cyclone models are unable to pick this rapid intensification because they do not incorporate the ocean dynamics accurately. 
Initiatives towards Cyclones
  •  Government is carrying out a National Cyclone Risk Mitigation Project (NCRMP) with the help of the World Bank to upgrade cyclone forecasting, tracking, and warning systems in India
  • The government is also implementing the Integrated Coastal Zone Management Project (ICZMP) to improve national capacity for the implementation of comprehensive coastal management in India.
  • Lastly, Government also separated Structural (includes construction) and non-structural measures for effective disaster management of cyclones.
Suggestions
  • The cyclones must be closely monitored at higher resolution and accuracy using on-site platforms such as buoys and moorings.
    • A buoy is a type of object that floats in water and is used in the middle of the seas as locators or as warning points for ships.
    • A mooring is any permanent structure to which a vessel may be secured.
  • The Indian National Centre for Ocean Information Services (INCOIS) must be provided with greater autonomy, finance, and human resources. This would improve the collection and dissemination of data on cyclonic events.
  • There must be an incorporation of the global warming signals in the weather models that can help tackle the challenges of intense cyclones in the future.
Conclusion

Climate projections indicate that the Arabian Sea will continue warming due to increasing carbon emissions, resulting in more intense cyclones in the future. This calls for strengthening the disaster management framework in consonance with the Sendai Framework for Disaster Risk Reduction 2015-2030.

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