'Cyclones in the North Indian Ocean are gaining intensity and that too rapidly'

Dr Sridhar Balasubramanian, associate professor in the Department of Mechanical Engineering at IIT Bombay, holds an adjunct faculty position in the IDP Climate Studies Centre. Photo: Dr Sridhar Balasubramanian

A week ago, Mumbai experienced the intense Cyclone Tauktae, which caused loss of life and property. Several neighbourhoods reported treefall and outages of electricity, phone networks, and internet, which went on for as many as four days in areas such as the Vasai-Virar belt. Worse, the impact of the disaster sank a barge named Papaa305 (P305) 40 nautical miles west of the Mumbai coast, claiming at least 70 lives.

Cyclone Yaas is expected to hit West Bengal on the evening of May 26 and could be as destructive as last year's Amphan, experts have said. While the east coast of India is known to experience such damaging cyclones quite regularly, the scenario on the west coast had been different not long ago. Before the recent Tauktae, Maharashtra saw Cyclone Nisarga affect the city in 2020. That was the second cyclone in 10 years to reach close to the coastal city of Mumbai, after Cyclone Phyan in 2009. Trends in the region have changed such that the frequency and intensity of cyclones have been increasing in the last 10 years. Scientists say more, and intense, cyclones are expected in the coming years.

Dr Sridhar Balasubramanian, an associate professor in the Department of Mechanical Engineering at IIT Bombay, holds an adjunct faculty position in the IDP Climate Studies Centre on the campus. His research interests primarily revolve around studying the atmosphere and ocean dynamics. Mid-Day.com reached out to the scientist to understand the warming of the Arabian Sea, how it affects cyclones originating near the west coast of India, and what the city of Mumbai can do to prepare for such climatic events in the future.

Here are edited excerpts from the interview:

It has been reported that the number of cyclones occurring on the west coast of India have been increasing over the last few decades. What is the reason behind the changing trend?

There is no doubt that the cyclone frequency near the west coast of India has increased over the last decade or so. This trend is mainly attributed to a paradigm shift in the dynamics of Arabian Sea. For a long time now, Arabian Sea was a relatively calmer basin in comparison to the Bay of Bengal. But in the last couple of decades, it is seeing some anomalous warming. The average sea surface temperature (SST) that used to be around 270-280C has now shot up to nearly 290-300C, which is significant. In simple terms, when the temperature of water increases, then its convective ability with the surrounding air is enhanced and so is the moisture content (which leads to formation of thunderclouds). Cyclones, which are a massive cluster of thunderclouds, feed off enhanced convection and moisture and this clearly explains the reason for the increased number of cyclones in the Arabian Sea.

Secondly, the wind patterns are also changing. Systems that used to make landfall over the Gulf region are now moving closer to the west coast of India, thereby resulting in a substantial increase in the number of unseasonal and extreme events.

How is the current situation different versus how cyclones originating in the Arabian Sea behaved in the past?

Cyclones in Arabian Sea usually have a tendency to move west towards Somalia, Oman or Yemen. This is because the upper-level wind patterns from the equator, i.e., 00N, to 200N are predominantly easterlies (meaning they push the system from east to west). However, of late this trend has changed, where systems are getting pushed towards the east, thereby impacting India.

Additionally, if you look at the genesis location of cyclones in Arabian Sea, then most of the cyclones used to form in the Central Arabian Sea, which allowed it to move to the Arabian Gulf. However, lately we are seeing the genesis of cyclones very close to the Lakshadweep region that travel very close to us, landfalling over Maharashtra or Gujarat. This is another indication of the ongoing shift in the warming patterns in the Arabian Sea.

What does the warming of the Arabian Sea have to do with the increase in the number of cyclones? Can you explain the science behind it?

In very simple language, when the temperature of water is increased, the convection with the surrounding air is enhanced and so is the moisture availability. This could be easily realised with a simple kitchen experiment, where you heat water at different temperatures.

Enhanced convection and moisture are fuel for any cyclone, which clearly explains the reason for increased number of cyclones.

Are these cyclones also gaining in intensity? What are your observations?

There is no doubt about it. Cyclones are gaining intensity and that too rapidly. Scientists worldwide are astounded by the rapid intensification of cyclones, especially in the North Indian Ocean. Cyclones such as, ‘Amphan', ‘Gati', ‘Nisarga', and most recently ‘Tauktae', all showed signatures of rapid intensification. One potential reason, apart from warmer temperatures, could be the role of atmospheric waves that govern the vorticity deposition in these systems. We had done some analysis on the role of waves on cyclone genesis and intensification. However, more active research is needed to understand the exact science behind such rapid intensification of cyclones.

What are your predictions for the next few years? Will more cyclones be seen along the west coast of India and how should state governments think about preparing for them?

Cyclones have a great affinity to warm temperatures and high amounts of moisture from the ocean. Our oceans are a sink that absorb the heat released by greenhouse gases, and then slowly release it. We are warming at an alarming rate, which is already exhibited in the ocean temperature trends.

Therefore, it is probably a no-brainer that there is a high probability of more (intense) cyclones along the west coast of India. Some measures include building shelters and preserving the ecosystem that act as natural defenses. A climate- resilient framework is also the need of the hour so as to promote actions that ensure progress towards adaptation and mitigation to extremes.

Particularly for a city like Mumbai, do these cyclones pose a specific kind of danger? What should one be aware of during city planning?

Being a low-lying city, it is at a high risk to flooding due to extreme rains and storm surge. We have already witnessed what could happen when cyclones come very close to Mumbai and have been fortunate that none of those made a direct landfall. The so-called ‘peripheral effects' of a cyclone itself have been quite disastrous for a city like Mumbai. Therefore, our civic body should make the city resilient to cyclonic winds, storm surge, and floods. And they must do it swiftly, since we never know what is going to happen in the next three to five years.

Are cyclones landing closer to the coast than expected? If so, why?

The cyclones are not really landing closer to the coast than expected. Even in the past, cyclones in Arabian Sea and Bay of Bengal have made frequent landfall. So, this is not new or surprising. However, the new trends are the growing number, high intensity, and rapid intensification. Like I already said, we need to preserve our ecosystem and also create a robust climate-resilience framework.

What are the ecological actions that can help keep cyclones at bay? Some suggest mangroves can have a significant role to play, for instance.

We cannot stop cyclones from forming or alter their trajectory. They are natural systems that form and move depending on ocean and atmospheric conditions. Therefore, our primary contribution and focus should be on reducing the impact.

Preserving the mangroves is definitely a viable option but that alone may not be sufficient. We need to design and build levees, flood walls, and efficient pumping systems that would protect us from storm surges, tidal bores, and flooding.

Please share with us a little about how your personal interest in climate science began, and your experience so far with researching the subject in India.

My interest in this field began in my early days of graduation studies, wherein I was specialising in Geophysical Fluid Dynamics, a branch of science dealing with atmosphere and ocean dynamics. I was immediately drawn towards this subject since it has huge implications on weather and climate patterns. I have been fortunate to work and interact with some of the best minds in this field.

In the Indian context, the weather dynamics are highly intricate owing to a large number of governing factors, both dynamically (warm ocean/atmosphere, high moisture incursion, etc.) and geographically (presence of Western Ghats, Himalayas and proximity to the equator). Weather and climate forecasting models are replete with parametrisations. My research interest lies in developing new parametrisations, based on dynamical modeling, that could help improve predictive capabilities of such complex systems. My group also looks at multi-scale physics to improve the fundamental understanding, thereby giving some new insights/direction.

As far as my experience goes, there are numerous problems that need immediate attention. That said, our research community is moving in the right direction with skillful weather forecasts and comprehension of climate change patterns, so that we are better prepared.

Also Read: Cyclone Yaas likely to intensify into very severe cyclonic storm: IMD