Mumbai is sinking 2 mm every year, says new research

Among major local factors causing subsidence of land in Mumbai are groundwater extraction, mining, reclamation of natural wetlands and infra projects

Another research, conducted at IIT Bombay, has found a strong correlation between land subsidence and the proximity of the area to mangrove plantations and the coastline. (PTI Photo/Mitesh Bhuvad)

A new research has revealed that Mumbai is sinking by an average of 2 mm annually. Though global warming is one of the main reasons, it is not the only culprit. While global warming is resulting in the melting of ice at the poles at a faster rate, thereby causing rise in sea levels, a number of local factors too are responsible for Mumbai’s sinking.

According to the study, published in the peer-reviewed Geophysical Research Letters Journal in March, groundwater extraction, mining, reclamation of natural wetlands, infrastructure projects and ecological disturbances is leading to “land subsidence” in Mumbai.

Based on five-year observations

The study – ‘Subsidence in coastal cities throughout the world’ – says, “A significant portion of the city (Mumbai) is subsiding more rapidly than 2 mm/yr.” The observation has been made after measuring the subsidence rate in Mumbai between 2015 and 2020.

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However, the rate of subsidence in Mumbai is significantly lower than in other countries in South Asia. For instance, Tianjin in China is the fastest sinking coastal city in the world at a rate of 5.2 cm per year, according to the study.

The study measured land subsidence in 99 countries globally. Besides Tianjin and Mumbai, the other coastal cities that are sinking include Jakarta (3.44 cm per year) in Indonesia, Shanghai (2.94 cm per year) in China, and Ho Chi Minh (2.81 mm per year) and Hanoi (2.44 cm per year) in Vietnam.

IIT identifies two subsidence areas

Meanwhile, another research, conducted by the Centre of Studies in Resources Engineering at IIT Bombay, has identified two major subsidence areas in Mumbai — Vasai and Wadala. This research has found a strong correlation between land subsidence, groundwater extraction, and the proximity of the area to mangrove plantations and the coastline.

“A densely populated and irregularly constructed slum area along the Ghatkopar-Mankhurd Link Road merging with the Sion-Panvel Expressway also shows subsidence in the range of 60mm over the same period,” the study adds.

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Explaining the implications of land subsidence, Sudha Rani NNV, lead author of another IIT Bombay study, told CNBC, “With sea levels projected to rise by around 1 to 1.2 metres in a high emissions scenario, we found that nearly 38 per cent Mumbai’s land may be inundated during normal rainfall. This is a severe issue that has to be addressed immediately.”