Is Mumbai prepared to weather the soaring sea level?

As the world grapples with the ever-pressing threat of climate change, cities across the globe are forced to confront the reality of rising sea levels. Among these urban centres, none is more vulnerable and yet resilient in its response than the bustling metropolis of Mumbai. In the wake of mounting concerns over climate-induced catastrophes, this coastal city has embarked on a journey towards fortifying its infrastructure.

Mumbai, often referred to as the financial capital of India, is uniquely positioned along the Arabian Sea, bearing the brunt of nature's fury during monsoon seasons. Its low-lying topography and densely populated areas make it exceptionally susceptible to the encroaching tides.

According to a World Meteorological Organisation report, at least nine Indian states are at high risk of sea level rise including Maharashtra. Mumbai faces a significant risk due to its vulnerable position with a 7,516.6 km long coastline.

Between 2013 and 2022, sea levels have risen at an average rate of 4.5 millimetres (mm) per year, as reported by the WMO. This rate of increase is three times higher than the rate observed between 1901 and 1971.

The consequences of sea-level rise are substantial, affecting small islands, coastal ecosystems, infrastructure, and human populations. These risks are expected to persist and increase beyond the year 2100. According to the report, taking rapid and sustained actions to reduce greenhouse gas emissions will help mitigate further acceleration of sea-level rise and its long-term projections.

The spectre of rising sea levels, exacerbated by global warming, has pushed the city to initiate a series of projects aimed at safeguarding its future.

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Mumbai Climate Action Plan

Mumbai's civic body - Brihanmumbai Municipal Corporation - along with the Government of Maharashtra and other stakeholders charted out a Mumbai Climate Action Plan. The MCAP is divided into six components - sustainable waste management, sustainable mobility, energy and buildings, air quality, urban greening and biodiversity and urban flooding and water resource management.

According to the MCAP, assessment of the urban flooding risk relies on analysis of two key parameters: extreme rainfall events (ERE) and flood risk mapping. The ERE analysis, conducted over a ten-year period, examines precipitation data from 37 automatic weather stations managed by the BMC. This assessment evaluates the interannual variation, intensity, and spatial concentration of extreme rainfall events during the June-July-August (JJA) months. The four-year period between 2017-2020, according to the MCAP's vulnerability report, has seen a steady rise in extremely heavy rainfall events.

The flood risk analysis considers data from BMC's disaster management department, including waterlogging/flooding hotspots, flood shelters, and the city's stormwater drainage network. South and Central Mumbai exhibit a higher concentration of flooding hotspots, particularly in areas with informal settlements, making them vulnerable to overlapping risks.

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Flood shelters are strategically located across the city; however, during a flood event, the effective accessibility of these shelters may reduce significantly, the analysis said.

Meanwhile, the coastal risk assessment - which includes the study of sea surface temperature (SST) patterns, tidal gauge measurements, and storm surges - has shown a steady increase over the last two decades in the Arabian Sea, potentially contributing to more cyclonic events. However, no statistically significant trends in sea level variations were observed between 2003 and 2020.

The analysis also considers the impact of storm surges, with events like Cyclone Kyarr-2019 and Cyclone Tauktae-2021 causing substantial sea level rises during high tides. The transformation of mangrove areas, which act as natural buffers against storm surges, has been observed, with efforts made to protect and expand mangrove cover.

Speaking on the projects the civic body has undertaken, P Velasaru, BMC Additional Commissioner (Projects) said that they have already begun implementing projects which will prevent coastal flooding.

"The BMC is studying models [adopted to combat rising sea levels] of nations like the Netherlands and has been using methods like installation of floodgates. We are planning to install 20 floodgates in the Mithi River and we will study the impact of the same and decide whether the same can be followed with other rivers in the city. Meanwhile, a Memorandum of Understanding has been signed with an American varsity - University of Notre Dame - to study the regional risk of rising sea level which will help us devise preventive measures accordingly," said the senior BMC official.

He further stated that the research, within five years' time, will be more accurate and thus assist in planning better.

Elucidating further, he said that the BMC is also working towards redeveloping all the informal living arrangements in the city into formal housing. "Slum areas are susceptible to the sea level rise and on that front, BMC has been working towards developing the slums into formal settlements and this will be realised within the next 10-15 years. It will also help minimise the risk," he added.

How does the city protect its coast?

A BMC source while elucidating on protection of coastline said that the Coastal Zone Management plans are drawn referring to the Coastal Regulation Zone notification from the Union government.

The source said that as per the present Development Plan of the city, the seaward side of the High Tide Land is protected under the tag of natural area. The HTL refers to a line on land up to which the highest water line reaches during the spring tide.

"The mangroves, beaches, saltpan lands and mangroves in the city come under No Development Zone. The rivers and nullahs are also protected as they have been marked under the green belt," they added.

Meanwhile, Aarey Colony was put under a Green Zone from NDZ. The Green Zone which was created in DP 2034, states that one must seek permission from the state government and Environment ministry before carrying out development work in the green lung of Mumbai.

When asked about the communities' involvement in drawing these plans, the BMC source said, "Nothing is approved without public consultation." They said that after plans are drawn by the authorities, the draft is made public and objections from residents are invited. To address the concerns mentioned in these applications, they said, a committee of experts is constituted by the Maharashtra government which also consists of some members from the BMC. The members usually have expertise in administration, transport, housing etc.

The source, speaking about the local communities whose livelihood depends on coastal regions, explained that CRZ regulations make special provisions for the ‘koliwadas' and ‘gaothans'. The communities living along the coast have been permitted to carry out traditional fishing and allied activities.

What do environmentalists think?

Environmentalists however think that the government is ignorant to the needs of local communities. Debi Goenka - an environmentalist and Executive Trustee of Conservation Action Trust - said that the government only involves the local communities when forced to do so.

In MCAP's vulnerability assessment report, it is mentioned mangrove areas become natural buffers against storm surges. When asked about its importance in the city's coastal resilience strategy, Debi said, "Mangroves are extremely important in mitigating extreme climatic events such as tsunamis and cyclones. They also sequester large quantities of Carbon. However, unless they are given room to expand landwards, the mangroves will disappear along Mumbai's coastline with rising sea levels once their roots are permanently flooded."

Debi further said that the protection of mangroves, mud flats, corals and saltpan lands would help Mumbai withstand extreme climatic events and aid in reducing pollution. "The growth of mangroves is being monitored by concerned citizens and a few forest officers because of Court Orders," he further stated.

Meanwhile, Stalin D, director of Vanashakti, also echoed that mangroves were the frontline defence against sea level rise and coastal erosion. He added, "Vanashakti undertakes mangrove plantations and cleanups with the active support of the coastal community members. We have successfully restored barren patches of mangroves and also reintroduced rare species in the Thane Creek belt. We use ground verification and satellite imagery to compare the outcomes of our interventions. Our organisation is one of the partners with Maharashtra State Forest Department mangrove cell for mangrove-related conservation activity. "

Goenka pointed out that there is no official mechanism for the citizens to get involved in the initiatives to protect Mumbai's coastline. Citizens can volunteer with NGOs who are active in this field, he remarked. Stalin reiterated the same and added that the citizens could also assist in organising awareness programs in their areas and raise funds for conservation efforts.