How Cyclones Over the North Indian Ocean Have Changed — and Why the Risk Is Growing

Cyclonic disturbances over the North Indian Ocean — covering the Arabian Sea, the Bay of Bengal, and adjoining land areas — have undergone profound changes over the last century. While the total number of disturbances has declined from mid-20th century highs, their geography, intensity and timing have shifted in ways that make them more destructive and harder to manage. These trends matter deeply for India’s disaster preparedness, coastal planning and climate adaptation strategy.

A century-long arc: fewer cyclones than before, but not a simple decline

Long-term data from 1900 to 2025 shows that cyclonic disturbances follow an inverted U-shaped trend. In the early decades of the 20th century, the North Indian Ocean averaged fewer than 10 disturbances annually. Activity rose sharply through the 1930s, stabilising at over 15 disturbances per year until the 1970s.

This period marked the most cyclone-active phase in the historical record. The subsequent decades, however, saw a pronounced decline. By the 2000s, the 10-year rolling average had fallen to around eight — the lowest in over a century. Although the 2010s and 2020s show a rebound, today’s activity remains well below the mid-century peak.

The Bay of Bengal slowdown and the Arabian Sea rise

The overall decline masks a sharp regional divergence. The reduction in cyclonic disturbances is driven almost entirely by falling activity in the Bay of Bengal, historically the most prolific cyclone basin in the region. Its declining output has pulled down the North Indian Ocean average.

In contrast, the Arabian Sea has seen a clear increase in disturbances. While its absolute numbers are still lower than the Bay’s, the upward trend is unmistakable. This rebalancing of cyclone origins is particularly significant because storms forming over the Arabian Sea behave very differently — and often more dangerously — than their Bay of Bengal counterparts.

Fewer storms, but far more intense ones

The most consequential shift lies not in how many disturbances form, but in how many intensify into powerful cyclones. A disturbance typically begins as a low-pressure area and may strengthen through depressions into cyclonic storms and, at the upper end, very severe, extremely severe or super cyclonic storms.

Since the 1970s, the proportion of disturbances in the Bay of Bengal that intensify into severe cyclonic storms or higher categories has risen markedly. More strikingly, disturbances originating in the Arabian Sea have historically had a higher likelihood of intensifying into severe storms than those in the Bay.

With the Arabian Sea now generating more disturbances, this higher intensification rate translates directly into greater regional risk. Coastal states on India’s western seaboard, once considered relatively sheltered, now face cyclones of a strength rarely seen in earlier decades.

Warming seas and unpredictability

The intensification trend is closely linked to ocean warming. Warmer sea surface temperatures provide more latent heat energy to tropical systems, allowing storms to strengthen rapidly and follow less predictable tracks.

Observations show that the Arabian Sea is warming faster than the global average. This has two consequences: cyclones gain strength more quickly, and forecasting their paths becomes more uncertain. For disaster managers, this shortens response windows and raises the stakes for evacuation and preparedness.

A seasonal shift towards the year’s end

Equally important is the changing timing of cyclones. Historically, Bay of Bengal disturbances clustered in the July–September monsoon window. Since the 1980s, this pattern has shifted decisively.

An increasing share of cyclonic disturbances now originate in the final quarter of the year — October to December. This post-monsoon concentration complicates disaster response, as it coincides with retreating monsoon systems, agricultural harvest cycles, and heightened coastal economic activity.

Why these trends change India’s risk profile

Taken together, the four trends — declining frequency, regional redistribution, rising severity, and shifting seasonality — paint a more dangerous picture than raw cyclone counts suggest. India is not facing more storms than in the past, but it is facing storms that are stronger, less predictable, and increasingly affecting previously lower-risk coastlines.

For agencies such as the “India Meteorological Department”, this means forecasting models must adapt to new climatic baselines. For policymakers, it underscores the urgency of climate-resilient infrastructure, coastal zoning reform, and early-warning systems that account for late-season, high-intensity cyclones.

The climate signal behind the statistics

The evolving cyclone regime over the North Indian Ocean reflects a broader climate reality: warming does not simply mean “more” extreme events, but different ones. As oceans heat unevenly, risks shift geographically and temporally.

Understanding these patterns is essential not just for disaster response, but for long-term planning — from ports and power plants to fisheries and coastal livelihoods. In the decades ahead, India’s challenge will not be counting cyclones, but living with stronger ones arriving at unexpected times and places.