Explained: Why is Mumbai Facing its First Cyclone in a Century?

Is climate change the key reason why cyclones like Nisarga have intensified over the last few decades?

NDRF, Navy, fire brigade and the BMC prepare for Cyclone Nisarga. 

(Photo: The Quint/Shruti Mathur)

Mumbai is about to be hit by a cyclone for the first time in a century. Cyclone Nisarga is expected to make landfall on Wednesday, 3 June, and will directly impact Maharashtra and Gujarat. With coastal Maharashtra bracing for a wind speed of 100-120 kmph and heavy to extremely heavy rainfall likely in isolated regions of Maharashtra, the state government’s disaster management teams are scrambling to prepare for the onslaught.

While cyclones forming across the Bay of Bengal and wrecking the coastlines along West Bengal and Odisha are relatively common, what has changed along the coastline of Maharashtra that’s causing a similar phenomenon? Read on to find out.

How Are Cyclones Caused?

Let’s get the basics out of the way. Sea surface temperature is the key reason for cyclones. When the temperature crosses 27 degrees Celsius, cyclogenesis kicks off. The warm, moist air over the ocean rises upwards from the surface. As the air moves up and away, there’s less air left on the ocean surface. This creates an area of lower air pressure below.

As the warm and moist air rises, clouds are formed. As the process continues, the clouds grow and so does the wind spin. As the storm rotates faster, an eye forms at the centre. Depending on how high the storm surge is, a cyclone can cause minimal or catastrophic damage at landfall.

Due to atmospheric conditions like warm sea temperature and wind conditions, the Bay of Bengal is more prone to cyclogenesis than the Arabian Sea, said Dr Roxy Mathew Koll, a scientist with the Indian Institute of Tropical Meteorology and Lead Author of IPCC Oceans. The latest in a series of dangerous cyclones to have hit the coastal states along the Bay of Bengal was Amphan that killed many and left thousands homeless.

“If you take the Arabian Sea, the ocean is generally cooler than the Bay of Bengal and also has opposing winds in the atmosphere, especially during early monsoon or during monsoon. At the lower level of atmosphere, the winds may be blowing in one direction and on the upper level, it may be blowing in the opposite direction. This prevents the cyclone from developing vertically upwards.”

Dr Roxy Mathew Koll, Scientist, Indian Institute of Tropical Meteorology, Lead Author, IPCC Oceans and Cryosphere

This is the key reason for states like Maharashtra and Gujarat to have been relatively unscathed by cyclones in the past. But that is changing now, all thanks to global warming.

Is Climate Change Causing Cyclone Nisarga?

After much research, scientists agree that yes, climate change is one of the main reasons why cyclones have become stronger over the last few decades. For one, climate change has caused an increase in the temperature of the sea surface. Since cyclones are fueled by heat, warmer seas mean more wind going upwards from the sea surface, causing higher wind speed, resulting in the storm emerging stronger.

Dr Koll said, “As a result of the rapid warming trend, even when the atmospheric conditions are not that favourable, like the early monsoon period is not at all favourable for cyclones to develop but the ocean conditions we see are quite favourable for intensification of such kind of systems, from low pressure systems to depression and then a cyclone.”

“In this case, prior to the formation of a cyclone, the Arabian Sea was quite warm, between 30-32 degree Celsius as recorded by some bouys installed in the Eastern Arabian Sea region.”

Dr Roxy Mathew Koll, Scientist, Indian Institute of Tropical Meteorology, Lead Author, IPCC Oceans and Cryosphere

Dr Koll pointed out that temperatures in the Bay of Bengal were between 30-33°C prior to Cyclone Amphan.

Global warming due to carbon emissions has also played a crucial role. The warm atmosphere causes higher water retention, this in turn leads to heavy rainfall and when coupled with a cyclone, cities are extremely prone to flooding.

How Will Nisarga Impact Mumbai?

Mumbai is no stranger to heavy rains and waterlogging. Every monsoon, low-lying areas of the city such as Hindmata, and areas in Dadar, Sion, Kurla, Santacruz among others, experience deluge. When coupled with a high tide, the water logging only gets worse.

“These cyclonic events are very unpredictable, so one doesn’t know the severity as it moves forward, what happens to them. So, we really have to wait and watch,” said Dr Anjal Prakash, Research Director and Adjunct Associate Professor, Bharti Institute of Public Policy, ISB. But waterlogging is a very strong possibility.

The impact of the waterlogging that is likely to ensue could have only been countered had the State implemented the recommendations of the Madhav Chitale Committee after studying the 2005 Mumbai floods that claimed thousands of lives. The committee came up with four key observations and recommendations.

“First, they said that the drainage lines in Mumbai were inadequate. Second, whatever available drainage line was there, a lot of them have been blocked or closed up by the societies or slum areas. Third, they also found that the water retention capacity of the city, that had many small ponds and reservoirs that used to actually act as a flood control, those areas have been systematically destroyed and new buildings have come up.”

Dr Anjal Prakash, Research Director and Adjunct Associate Professor, Bharti Institute of Public Policy, ISB

Aside from encroachment, Mumbai has also lost a large chunk of its mangroves over the last few decades. These mangroves are usually the first line of defence when battling natural disasters like cyclones and flooding.

Also, the timing of Cyclone Nisarga couldn’t have been worse. The ‘maximum city’ has been the worst-hit due to the COVID-19 crisis. With over 42,200 cases as of 2 June, the city’s hospitals have been overwhelmed under the surging demand for healthcare facilities. At a time like this, maintaining social distancing while battling the crisis could pose an additional challenge.

What are the Precautions Taken by the State?

Maharashtra Chief Minister Uddhav Thackeray held review meetings with the departments overlooking preparedness for the cyclone on Tuesday, 2 June. The CM appealed to citizens to stay indoors for the next two days. Cabinet Minister Aditya Thackeray shared on Twitter that he held a detailed review meeting with top IAS officers in the BMC.

To ensure the safety of residents, 34 National Disaster Response Force (NDRF) teams have been deployed across Maharashtra, Gujarat, Daman and Diu and Dadra and Nagar Haveli. In Maharashtra, NDRF teams have been deployed at locations like Mumbai, Palghar, Thane, Raigad, Ratnagiri, and Sindhudurg. Earlier during the day on 2 June, the coast guard instructed fishermen to return to the shore.

The Western Naval Command has been alerted as well.

“In Mumbai, the Maharashtra Naval Area will be on standby with five Flood Rescue Teams and three Diving Teams throughout the monsoon season. These teams are stationed at various naval areas across the city to enable early response over a larger area. The teams are fully equipped and have been trained for rescue operations.”

Statement by the Indian Navy 

Fire brigade personnel on standby along the beach.(Photo courtesy: Prabhat Rahangdale, Chief Fire Officer)

The Mumbai Police released an order prohibiting any presence or movement in places along the coast like beaches, promenades, parks, and other places along the coastline. Mumbai fire brigade, too, is on alert. Twelve teams of brigade personnel and rescue boats have been kept on standby.