Cyclonic disturbances over the North Indian Ocean — encompassing the Arabian Sea, the Bay of Bengal and adjoining land regions — have undergone fundamental changes over the last hundred years. Long-term data reveal not a simple rise or fall in storms, but a reorganisation of when cyclones form, where they originate, and how destructive they become. These shifts carry major implications for India’s disaster preparedness and climate adaptation strategies.
A century-long shift in cyclone frequency
Cyclonic activity since 1900 displays a clear inverted U-shaped trend. In the early decades of the 20th century, the 10-year rolling average of disturbances remained below 10 per year. This rose sharply by the 1930s, crossing 15, and stayed broadly stable until the 1970s. The following decades witnessed a pronounced decline, with activity reaching a low point in the 2000s when the average dropped to around eight. Although the 2010s and 2020s show a gradual rebound, current levels remain significantly lower than mid-century highs, signalling a long-term structural change rather than short-term variability.
Why the Bay of Bengal’s decline reshapes totals
The overall fall in cyclonic disturbances is driven almost entirely by a sharp reduction in activity in the Bay of Bengal, historically the most prolific cyclone-generating region in the North Indian Ocean. Its reduced output has pulled down aggregate numbers. In contrast, the Arabian Sea has seen a steady rise in disturbances. While still less active than the Bay, this upward trend marks a redistribution of cyclone risk towards India’s western coastline.
Intensity rising even as numbers fall
A critical transformation lies in cyclone severity. Disturbances that once dissipated as low-pressure systems or depressions are now increasingly intensifying into severe cyclonic storms and beyond. Since the 1970s, the proportion of severe storms in the Bay of Bengal has risen steadily. Historically, systems originating in the Arabian Sea have been more likely to reach very severe or extreme categories. As Arabian Sea disturbances become more frequent, this higher propensity for intensification significantly elevates regional risk.
Warmer seas and faster intensification
Ocean temperatures play a decisive role in cyclone development. Warmer waters provide more energy, allowing storms to strengthen rapidly and follow less predictable tracks. Evidence indicates that the Arabian Sea is warming faster than the global average. This has led to cyclones that intensify closer to land, compressing warning times and increasing threats to coastal populations, ports, fisheries, and offshore infrastructure.
A changing cyclone calendar in the Bay
The seasonality of cyclonic disturbances has also shifted markedly. Until the 1980s, most Bay of Bengal systems formed during the July–September monsoon months. Since then, cyclone genesis has increasingly moved to the October–December period. This post-monsoon concentration overlaps with harvest seasons and peak fishing activity, compounding socio-economic vulnerability and stretching disaster management systems beyond traditional planning windows.
Why these trends demand policy attention
Together, these four shifts — fewer storms, changing geography, greater intensity, and altered seasonality — challenge long-standing assumptions based on historical averages. India now faces a future of fewer but more destructive cyclones, emerging risks along the west coast, and storms striking outside conventional seasons. Infrastructure standards, early warning mechanisms, coastal zoning, and climate resilience planning must adapt to this evolving cyclone regime.
What to note for Prelims?
- North Indian Ocean cyclone basins and their characteristics
- Cyclone intensity classification based on wind speeds
- Contrasting cyclone behaviour of the Bay of Bengal and Arabian Sea
- Link between sea surface temperature and cyclone strength
What to note for Mains?
- Climate change and structural shifts in cyclone patterns over India
- Implications of declining frequency but rising intensity for disaster governance
- Emerging cyclone risks for India’s western coastline
- Policy challenges posed by changing cyclone seasonality
