Cyclone Arnab And The Influence Of El Nino

Source: Indian Express
GS I: Geography

Why in the News?

Cyclone Arnab brought heavy rainfall and flooding to parts of Andhra Pradesh and Odisha. The event highlights the influence of El Nino on tropical cyclone formation, intensity and movement.

News in Brief

• Cyclone Arnab caused heavy rainfall, flash floods and waterlogging in coastal Andhra Pradesh and Odisha. Several districts were placed under weather alerts.
• The cyclone developed over the Bay of Bengal and intensified into a very severe cyclonic storm before making landfall near the Andhra Pradesh coast.
• El Niño alters sea-surface temperatures and atmospheric circulation over the tropical Pacific and Indian Ocean, influencing cyclone behavior.
• Odisha and West Bengal are generally more exposed to Bay of Bengal cyclones. During some El Niño years, cyclone activity can shift towards the Andhra Pradesh and Tamil Nadu coasts.

How did cyclone Arnab intensify?

• Cyclone Arnab originated as a low-pressure system over the southeast Bay of Bengal on October 23 and intensified into a cyclonic storm by October 26.
• It subsequently strengthened into a very severe cyclonic storm, with wind speeds increasing from around 125 kmph around 185 kmph.
• The cyclone moved towards the Andhra Pradesh coast faster than initially forecast.
• After crossing the coast between Repalle and Vishakhapatnam, it weakened as it moved inland.
• Heavy rainfall affected coastal Andhra Pradesh and Odisha, with flooding and damage reported in vulnerable areas.

How does El Nino influence cyclones?

• El Nino is the periodic warming of the central and eastern equatorial Pacific Ocean.
• It alters atmospheric circulation, wind patterns and rainfall distribution across the tropics.
• Its influence on tropical cyclones includes;
  • Changes in wind patterns: El Niño can alter large-scale atmospheric circulation and vertical wind shear, affecting cyclone formation and intensification.
  • Ocean temperatures: Warm ocean water supplies the heat and moisture needed to fuel tropical cyclones.
  • Regional variations: El Niño can influence where cyclones form and the direction in which they move, although the response differs between ocean basins.
  • Indian Ocean influence: Changes in atmospheric circulation and the Indian Ocean’s thermal conditions can affect cyclone activity in the North Indian Ocean.
• El Nino does not necessarily increase cyclone activity everywhere.
• Its effects depend on regional sea-surface temperatures, wind shear, atmospheric circulation and other climate conditions.

Why does Cyclone activity shift along India’s East Coast?

• Odisha and West Bengal are particularly exposed to cyclones originating in the Bay of Bengal.
• During certain El Niño years, changes in atmospheric circulation and cyclone tracks may favour impacts along the Andhra Pradesh and Tamil Nadu coasts.
• In 2014, Cyclone Hudhud affected the Andhra Pradesh coast, illustrating the potential for severe cyclones to impact this region.
• However, cyclone tracks are not determined by El Niño alone.
• Individual storm paths depend on surrounding pressure systems, steering winds and other atmospheric conditions.

Tropical Cyclones and Their Energy Source

• Tropical cyclones develop over warm ocean waters and derive energy from the transfer of heat and moisture from the sea to the atmosphere.
• Conditions favorable for cyclone development include;
  • Warm sea-surface temperatures: Generally around 26.5°C or higher over a sufficient depth of water.
  • High atmospheric moisture: Supports the development of deep convective clouds.
  • Low vertical wind shear: Allows the storm’s vertical structure to remain organised.
  • A pre-existing low-pressure system: Provides the initial disturbance around which the cyclone can develop.
  • Sufficient Coriolis force: Helps the developing system acquire rotation.
• Cyclone Arnab reportedly intensified rapidly, highlighting the importance of favorable oceanic and atmospheric conditions.

How are tropical cyclones named?

• The naming of tropical cyclones in the Bay of Bengal and Arabian Sea began in 2004.
• The World Meteorological Organization (WMO) and the United Nations Economic and Social Commission for Asia and the Pacific (UNESCAP) support the regional cyclone-naming mechanism.
• The regional list contains names contributed by 13 member countries.
• The India Meteorological Department’s Regional Specialized Meteorological Centre (RSMC), New Delhi, officially assigns names to cyclones in the North Indian Ocean.
• Names are selected sequentially from the approved list.
• Once a name has been used, it is not repeated in the same list.
• Cyclone Arnab was named by Bangladesh while Murasu, proposed by India, was next in the sequence.
• Murasu is a Tamil word for a drum.

Cyclone movement and rainfall

• Tropical cyclones in the Northern Hemisphere generally rotate anticlockwise.
• Their movement is influenced by surrounding high and low pressure systems and large-scale atmospheric winds.
• Cyclones can intensify rapidly over warm waters but usually weaken after landfall because they lose their oceanic moisture and heat supply.
• Heavy rainfall may continue after landfall, causing flooding and landslides in vulnerable regions.
• Cyclone Arnab weakened after crossing the coast but continued to produce heavy rainfall over parts of eastern India.

Tropical Cyclones in the North Indian Ocean

• The North Indian Ocean includes the Bay of Bengal and the Arabian Sea.
• The Bay of Bengal generally experiences more tropical cyclones than the Arabian Sea.
• Warm waters, high moisture levels and favorable atmospheric conditions support cyclone formation.
• India’s east coast is particularly vulnerable to storm surges, coastal flooding and intense rainfall.
• The IMD is responsible for monitoring tropical cyclones and issuing warnings in the region.

Significance and Challenges for India

• Understanding cyclone behavior and climate drivers such as El Nino helps improve disaster preparedness, forecasting and timely evacuation, reducing casualties and property damage.
• It is also important for protecting agricultural crops, rural livelihoods and coastal infrastructure such as ports, roads and power networks.
• Strengthening early-warning systems, last-mile communication and community awareness can improve  resilience in cyclone-prone regions.

Challenges

• Rapid cyclone intensification and changes in storm tracks can make forecasting and evacuation difficult.
• Coastal settlements, fishing communities and vulnerable housing face greater risks from strong winds, storm surges and flooding, which may continue even after landfall.
• Moreover, El Niño alone cannot explain cyclone behaviour, as it depends on several interacting oceanic and atmospheric factors.

Way Forward and Conclusion

The IMD’s forecasting and rapid-intensification monitoring capabilities should be strengthened, alongside better coordination between central and state agencies. Integrating ENSO forecasts with Indian Ocean conditions, improving early-warning communication for coastal communities and enforcing risk-sensitive land-use planning can reduce cyclone-related losses.

At the same time, resilient coastal infrastructure, mangrove restoration and community awareness are essential for long-term preparedness. A combination of scientific forecasting, effective disaster management and ecosystem-based protection can strengthen India’s resilience to tropical cyclones.

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