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UPSC MainsGeneral Studies Paper IGeographyPractice question

Cyclone Vulnerability: Bay of Bengal vs Arabian Sea

Discuss why Bay of Bengal is more prone to cyclones than the Arabian Sea. Also explain the reasons for the decrease in frequency of tropical cyclones during south-west monsoon season.

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How to approach

Begin by comparing the historical cyclogenesis distribution between the Bay of Bengal and the Arabian Sea. Detail the oceanographic, atmospheric, and geographical reasons that make the Bay of Bengal more prone to cyclones, followed by an explanation of the meteorological factors suppressing cyclogenesis during the southwest monsoon. Conclude with a forward-looking perspective on climate change and disaster mitigation.

Model answer

432 words

Introduction

Historically, the Bay of Bengal accounts for roughly 80% of all tropical cyclones formed in the North Indian Ocean basin, compared to only 20% in the Arabian Sea. However, anthropogenic warming is altering these dynamics, resulting in a recorded 52% increase in cyclogenesis over the Arabian Sea in recent decades.

Why the Bay of Bengal is More Prone to Cyclones than the Arabian Sea

  • Oceanic Stratification and Freshwater Influx: The Bay of Bengal receives massive freshwater discharge from perennial river systems like the Ganga, Brahmaputra, and Irrawaddy. This low-salinity freshwater cap prevents vertical ocean mixing, trapping solar heat in the upper layer and maintaining high Sea Surface Temperatures (SSTs > 28°C), which act as an uninterrupted thermal engine for cyclones. In contrast, higher salinity and stronger winds over the Arabian Sea foster vigorous vertical mixing, drawing cooler deep waters upward.
  • Remnants from the Northwest Pacific: The Bay of Bengal regularly receives remnant low-pressure systems and depressions originating from typhoons in the South China Sea and Northwest Pacific Ocean. These systems cross Southeast Asia and regenerate rapidly over the warm waters of the Bay, supplying pre-existing vortex seeds.
  • Surface Wind Patterns and Topography: Surface winds over the Bay of Bengal are relatively calm compared to the gale-force southwest monsoon winds in the Arabian Sea, preventing rapid heat dispersion. Additionally, the concave, funnel-shaped coastal geography of the northern Bay of Bengal acts to converge winds and amplify storm surges.

Reasons for Decrease in Cyclone Frequency During the South-West Monsoon Season

  • Extreme Vertical Wind Shear: The onset of the southwest monsoon establishes the upper-tropospheric Tropical Easterly Jet (TEJ) over peninsular India. The sharp contrast between strong low-level southwesterly winds and high-altitude easterlies generates intense vertical wind shear, which tilts and shears convective columns, preventing storm structures from organizing vertically.
  • Northward Shift of the ITCZ: During the summer monsoon, the Inter-Tropical Convergence Zone (ITCZ), or monsoon trough, shifts deep into the northern Indian landmass (Indo-Gangetic plain). Consequently, the primary zone of low-level cyclonic vorticity moves away from the open ocean waters necessary for cyclone intensification.
  • Ocean Surface Cooling: Persistent monsoonal cloud cover limits insolation, while heavy precipitation and strong wind-driven coastal upwelling (notably the Findlater Jet off the Somali and Arabian coasts) lower sea surface temperatures below the critical threshold of 26.5°C required for cyclogenesis.

Conclusion

While the Bay of Bengal has historically borne the brunt of extreme cyclonic activity, warming oceanic basins are making the Arabian Sea increasingly turbulent. India’s disaster governance framework, spearheaded by the National Cyclone Risk Mitigation Project (NCRMP), must therefore shift from an East-Coast-dominated focus to an integrated, pan-coastal climate resilience strategy.

Key facts to remember

statistic

The Bay of Bengal historically accounts for roughly 80% of all North Indian Ocean cyclones, though recent decades have observed a 52% increase in cyclogenesis over the Arabian Sea.

— India Meteorological Department (IMD)
definition
Oceanic Stratification

The layering of ocean water caused by differences in salinity and density, such as when buoyant freshwater river discharge prevents vertical mixing with denser, colder subsurface water.

scheme
National Cyclone Risk Mitigation Project (NCRMP)

A flagship initiative aimed at upgrading structural and non-structural measures such as early warning systems, coastal shelters, and embankment protections across vulnerable coastal states and union territories.

Frequently asked questions

Why do tropical cyclones rarely develop in the peak of the southwest monsoon season?

The presence of the high-altitude Tropical Easterly Jet generates severe vertical wind shear over the oceans, which disrupts the vertical convective towers needed for cyclone development, while the monsoon trough shifts inland over the landmass.

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