Rising Sea Levels Put Mumbai, Kolkata at Risk, Millions Face Displacement

New Delhi: The climate crisis is moving closer to India’s biggest coastal cities, with Mumbai and Kolkata emerging as major hotspots in the global sea-level rise threat. A new United Nations assessment has warned that rising seas, combined with land subsidence, could intensify flooding and displacement across vulnerable parts of the Indian subcontinent.

The UN has identified Mumbai and Kolkata, along with Dhaka in Bangladesh, among low-lying South Asian cities facing growing risks from permanent inundation. More than 14 million people across these three urban areas are considered at immediate risk of losing their homes as sea levels rise.

The warning comes against a backdrop of accelerating global sea-level rise. According to the UN, the average global sea level increased by 4.7 mm annually between 2014 and 2023, before surging to a record 5.9 mm in 2024. Around 770 million people worldwide—roughly one in 10—live less than five metres above the high-tide line, putting them particularly close to the danger zone.

Mumbai faces a mounting coastal threat

Mumbai’s densely populated coastline and low-lying terrain make it particularly vulnerable to rising seas, tidal flooding and storm surges. The problem is further complicated by urban expansion and the loss of natural coastal buffers.

A World Bank assessment estimates that, without additional protective measures, the annual cost of coastal flooding in Mumbai’s urban areas could climb from $2.4 billion in 2010 to $21 billion by 2030 and $75 billion by 2050.

Under a moderate climate scenario, the World Bank projects Mumbai, Kolkata and Surat among the Indian cities facing substantial exposure. For Greater Mumbai, its modelling indicates that 210 sq km of settlements could be exposed by 2100, even if built-up areas remain at their 2015 boundaries—the highest projected exposure among the Indian cities examined.

The IPCC has also highlighted Mumbai’s enormous potential economic exposure, estimating $112–162 billion in sea-level-rise-related damages by 2050 under the cited scenarios. The assessment stresses that such figures illustrate possible impacts in the absence of adaptation rather than inevitable future losses.

Is Kolkata running out of time?

A new UN report says the city’s low-lying geography and ageing infrastructure make it acutely vulnerable to sea level rise

WION’s @ShreyaG9401 reports from the banks of the Hooghly pic.twitter.com/Fy9s6rOWIp

— WION (@WIONews) September 2, 2026

Kolkata caught between rising seas and sinking land

Kolkata faces a particularly complex challenge because its vulnerability is linked not only to rising seas but also to land subsidence.

Situated within the low-lying Ganges-Brahmaputra delta system, the city and surrounding areas are exposed to coastal flooding, extreme rainfall and tidal impacts. The IPCC lists Kolkata among major Asian coastal cities where sea-level rise and subsidence can combine to increase flood risks.

This creates a dangerous multiplier effect: if the land sinks while the sea rises, the effective increase in relative sea level can be greater, leaving communities increasingly exposed to flooding and waterlogging.

Asia bears the heaviest global burden

The danger facing Mumbai and Kolkata is part of a much larger Asian crisis. The IPCC identifies Asia as the world’s most exposed region to sea-level rise, with 12 of the 20 countries most exposed to sea-level-rise-related flooding located in the continent. China, India, Bangladesh, Indonesia and Vietnam are among the countries with the highest coastal population exposure.

Of the 20 major coastal cities projected to face the highest flood losses by 2050, 13 are in Asia. Kolkata and Mumbai are among the cities highlighted in the IPCC assessment, alongside Guangzhou, Ho Chi Minh City, Jakarta and Bangkok.

The latest UN assessment puts the global scale of the potential humanitarian crisis in stark terms. Up to 1.2 billion people could be displaced by 2050 without urgent adaptation measures, as rising seas threaten homes, livelihoods, freshwater supplies and critical infrastructure.

Beyond flooding, a threat to livelihoods

Sea-level rise is not simply a question of water entering cities. Saltwater intrusion can contaminate freshwater sources, agricultural land and groundwater, while repeated flooding can damage roads, hospitals, schools, drainage networks and other essential infrastructure.

For poorer and informal communities, the consequences can be particularly severe. Repeated flooding can destroy household assets, interrupt employment and make living costs unaffordable, potentially turning gradual environmental pressure into large-scale climate-driven migration.

The UN has warned that the consequences extend to housing, food, healthcare, sanitation, education and human rights.

A global warning for coastal cities

Mumbai and Kolkata are not isolated cases. Around the world, major cities including Miami, New York, Shanghai, Guangzhou, Bangkok, Jakarta and Ho Chi Minh City face varying degrees of exposure to rising seas, coastal flooding and land subsidence.

The IPCC warns that rising seas will continue for centuries even if greenhouse-gas emissions are sharply reduced. The question, therefore, is no longer whether sea levels will rise, but how much damage can be prevented and how many communities can be protected.

Experts point to stronger coastal defences, mangrove and wetland protection, improved drainage, early-warning systems, climate-resilient infrastructure and better urban planning as essential measures. In locations where protection ultimately becomes unviable, planned or managed retreat may become unavoidable.

For Mumbai and Kolkata, the warning is clear: the sea is rising, the risks are growing, and the window for preparing India’s coastal cities is narrowing.