A Tale of Two Seas
Historically, India's east coast has borne the brunt of cyclonic activity, with the Bay of Bengal being a far more active basin than the Arabian Sea. The Bay of Bengal traditionally experiences about four to five cyclones annually, compared to just one or two
in the Arabian Sea. However, recent studies are highlighting a significant and concerning shift in this pattern. While the Bay of Bengal remains a potent threat, the Arabian Sea is no longer the quiet neighbour it once was. This divergence is forcing scientists and disaster management authorities to reassess risks and rewrite playbooks for coastal safety.
The Arabian Sea's Troubling Transformation
The most startling change is occurring in the Arabian Sea. According to analysis, the frequency of cyclones in this western basin has increased by a staggering 52% in the last two decades (2001-2019). In contrast, the Bay of Bengal saw an 8% decrease in the same period. It’s not just about the number of storms but also their power. The Arabian Sea is now witnessing a significant increase in the frequency of 'very severe' and 'extremely severe' cyclonic storms, particularly in the post-monsoon season. Researchers attribute this directly to rising sea surface temperatures linked to global warming; the Arabian Sea has warmed by as much as 1.2 to 1.4 degrees Celsius over the last four decades, providing the extra heat energy needed to fuel more powerful storms.
Bay of Bengal: A Familiar But Evolving Threat
While the total number of cyclones may have slightly decreased in the Bay of Bengal, it remains an incredibly dangerous region. The bay's semi-enclosed nature, higher surface temperatures, and lower salinity have always made it a fertile breeding ground for cyclones. The new danger lies in the changing characteristics of the storms that do form. Studies suggest that climate change is increasing the potential for rapid intensification, where a storm can escalate from a weak cyclone to a very severe one in a matter of hours. A warmer atmosphere can hold more moisture, leading to cyclones that unleash more intense rainfall upon making landfall, as seen with recent storms like Cyclone Arnab.
The Science Behind the Shift
The primary driver behind these changes is a warming climate. Oceans absorb over 90% of the excess heat trapped by greenhouse gases. This warming is not uniform. The Indian Ocean is warming faster than other tropical basins, creating conditions ripe for more intense storms. This added heat energy allows storms to form more quickly, sustain their power for longer, and carry significantly more moisture. Furthermore, atmospheric conditions are changing. Some research points to weaker vertical wind shear—the change in wind speed and direction with height. Strong wind shear can tear a budding cyclone apart, but weaker shear, which is being observed more frequently, allows the storm's structure to grow organised and powerful.
Why These Regional Differences Matter
Understanding this coastal divergence is critical for protecting lives and infrastructure. For decades, India's west coast had relatively less robust cyclone mitigation infrastructure compared to the east coast, simply because the threat was lower. The sharp increase in cyclone frequency and intensity in the Arabian Sea means states like Gujarat, Maharashtra, and Kerala must rapidly adapt their preparedness strategies. It requires building new cyclone shelters, strengthening early warning systems, and educating a population less accustomed to such severe weather. For the east coast, the challenge is different. It involves upgrading existing systems to handle storms that intensify faster and produce more extreme rainfall, leading to greater risks of storm surge and inland flooding. A one-size-fitsall national strategy is no longer sufficient.
