India’s Coastal Cities Face Heavy Flooding Risk Due To Sea Level Rise

Globally, the mean sea level has risen by 20 cm since 1800, and is now rising at a rate of 3.22 millimetre (mm) in recent years. Estimates suggest this could increase by up to 1 metre (or 100 cm) by the end of this century.

While these estimates are useful, local experience of this will differ due to variations in ocean currents and dynamics that can affect local water height, and phenomena such as land subsidence—necessitating a measure called the ‘relative mean sea level’ (RMSL).

A July 2025 study by the Indian National Centre for Ocean Information Services (INCOIS), a government body, estimated that—relative to the reference period or baseline of 1995-2014—India’s coastal cities will see an increase in RMSL between 62 cm in Vishakhapatnam and 87 cm in Bhavnagar by the year 2100.

Mean sea-level rise is one of the major consequences of global warming, threatening the existence of many low-lying coastal regions and islands worldwide. At the coasts, the mean sea level or baseline will fuse with storm surges and tides—such as during days of heavy rainfall—to cause changes in the coastal water level (of the order of a few metres) to produce extreme sea levels (ESL). Metropolitan cities including Mumbai, Kolkata and Chennai will be affected by this ESL rise, research shows. Such events will become more common and more deadly in the future.

India needs to urgently cut down on emissions and build infrastructure to protect its coastal cities from sea level rise.

IndiaSpend reached out to the Ministry of Earth Sciences on what urgent, targeted adaptation strategies is it planning for India's coastal cities, what are its immediate and mid-term action plans, whether it has allocated any funds for implementing crucial flood barriers and seawalls, whether it is providing any technical, financial, and data support to high-risk states, whether it will mandate city planning authorities for developing specific urban flood models. This story will be updated when we receive a response.

Bulging baseline

The Paris agreement aims to keep the earth from getting hotter by more than 1.5 degrees Celsius. The global Intergovernmental Panel on Climate Change (IPCC) is a body that assesses the science related to climate change. It looks at various scenarios of global warming including ones with high emissions and low climate action, vice versa, and those in between, and what each scenario means for the world we live in. IPCC has developed multiple such scenarios for the future which form the basis of the INCOIS report as well.

The INCOIS report uses information on the projected changes in the relative mean sea level, tides, and climate extremes to assess the projected changes in extreme sea levels for the end of this century along the Indian subcontinents and islands under a ‘medium challenges to mitigation’ scenario and a ‘high challenges to mitigation’ scenario. In simple terms, both these scenarios depict a situation each where the world managed to curb warming to a medium extent and to very little extent, respectively.

Vishakhapatnam could see between 40 cm and 62 cm rise in the RMSL based on the emissions pathway that will unfold, projections show. On the other hand, Gujarat’s Bhavnagar could see between 63 cm and 87 cm rise.

In addition, as we said, local phenomena such as tidal waves and storm surges could see Bhavanagar’s ESL rise by between 87 cm and 112 cm, reflecting the need for urgent action.

Source: Indian National Centre for Ocean Information Services, July 2025 report

Heavy rains in August had caused severe flooding in Vishakhapatnam this year and its district disaster management website labels coastal erosion as a chronic event.

For context, 1 mm is a grain of sand, 1 cm is a paper clip, 30 cm is a standard ruler, 60 cm is about the height of a suitcase, 90 cm is roughly a standard dining table, and 120 cm is the height of a healthy seven-year-old child.

In comparison, the island nation of Tuvalu has seen sea levels rising by 14 cm in the last 30 years and will see a further rise of 19 cm in the next 30 years which could cause serious flooding in the island. Countries like Tuvalu are under a grave threat of submersion due to sea level rise caused by global warming.

“Historically, the north Indian Ocean has been a hotbed for tropical cyclones, and the coasts of the Indian subcontinent are prone to storm surges and tidal maxima [highest tide] with a typical range of a few meters,” the INCOIS report said. “Notably, a large part of the coastal zones of the Indian subcontinent lies well within 5-10 meters of mean sea level.”

INCOIS has warned that the mean sea level will notably rise in the Indian islands of Minicoy and Port Blair under a high emission scenario, indicating the islands' vulnerability to ESL-driven hazards.

The mega problem in metropolises

To add to the INCOIS report, a new paper released in August by researchers from India and the UAE found that, in the period from 2030 to 2100, Mumbai, Kolkata and Chennai are at a high flooding risk due to extreme sea level.

Mumbai faces extensive flooding risks according to all emissions scenarios examined by the paper. “The flooding reaches its peak intensity across the coastal section and riverfront zones as extensive parts of the city’s urban facilities come under risk. The flooding area extends widely throughout the southern and eastern regions,” the paper noted.

Mumbai’s southern region hosts all the state’s important administrative buildings and its legislature. A new study this year had found how a larger section of Mumbai city is now prone to floods, 13 wards instead of 11, which house 61% of the city’s population. The city experienced flooding on several occasions this monsoon season.

Even Kolkata faces a similar risk.

“The location of Kolkata near both the Hooghly River and the Bay of Bengal leads the city to face severe flooding risks. Major flooding is predicted on riverbanks, together with coastal lowlands,” the paper noted. Although the flooding extent is reduced under low emission scenarios, coastal and riverbank regions remain at risk.

Under high-emission climate scenarios, “significant flooding risks are posed” to Chennai, “including its extensive coastal infrastructure and large resident population”, the paper said. Peak flood intensity is projected in two main areas: along the East Coast Road and within the urban waterfront region.

In the same vein, coastal areas of Vishakhapatnam will face extreme risk from rising sea levels while flooding will spread across its urban terrain. In medium-emission predictions, the waterfront sections of the city will be flooded, although to a more limited degree.

The geographical location of Mumbai, Kolkata and Chennai makes them vulnerable.

“Sea levels at these locations begin higher than other regions, and their risk response escalates much more when emission scenarios reach at their peak,” researchers noted. “The towns are expected to battle with coastal flooding problems, along with erosion issues, in addition to climate-related complications,” the paper stated, stressing the need for urgent action involving building up harbour defences and better drainage systems, combined with complete city adaptation strategies.

Future flooding hazards targeting Mumbai and Kolkata require immediate implementation of flood barriers along with seawalls and storm surge protection systems.

“Since these cities encounter major risks, it is crucial to embed climate-resilient infrastructure into their long-term urban planning systems as a defence against SLR. Mumbai, along with Kolkata, should adopt sustainable urbanisation policies to stop people from rapid building construction in coastal zones where high risks exist,” the researchers recommended and stated that medium-risk cities such as Kochi and Mangaluru should focus on strengthening natural flood barriers and early warning systems.

Need for urban flood models

The Union government has taken a number of steps to contain sea level rise and coastal flooding in smaller cities such as the implementation of a Coastal Management Information System (CMIS) to address the challenges of coastal erosion through data. Recognising the absence of a dedicated coastal data repository, CMIS was developed to “systematically collect and analyse key coastal parameters”.

Also, India has a National Centre for Coastal Research (NCCR) to map the shoreline changes along the Indian coast to enhance preparedness for storm surges, tsunami, etc. NCCR has prepared and published a status report on National Assessment of Shoreline changes along Indian Coasts in March 2022 which provides the status of India’s coastline by classifying them into ‘erosion’, ‘accreting’ and ‘stable’ coasts.

But safeguarding coastal infrastructure, freshwater sources, and livelihoods from flooding and saltwater intrusion in coastal regions is the responsibility of the respective state governments.

For example, in order to prevent coastal flooding in Mumbai, the Maharashtra government and Mumbai’s civic body have included building flood resilient systems and infrastructure, managing disaster risks in the Mumbai Climate Action Plan 2022.

“We have the necessary technology to work on coastal flooding but we need implementation,” said professor at IIT Bombay and IPCC author Subimal Ghosh.

“Cities like Mumbai need early warning systems, increase of storm water drainage network or their redesigning and interventions to expand their capacity. There needs to be a robust flood monitoring system for providing people with information, so that they can take decisions accordingly. Every city should have flood zonation and its specific urban flood model on which there should be multiple ‘what if’ scenarios. Then there needs to be a standard operating procedure on what needs to be done in each case,” said Ghosh.

He also pointed out how long term models that predict future sea level rise with specific details for cities have a lot of uncertainty built in even now, something both studies have also acknowledged.

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