Mumbai’s exposure to coastal flooding could worsen sharply in the coming decades as rising sea levels, land subsidence and extreme rainfall converge, putting the city’s homes, infrastructure and freshwater resources at increasing risk, according to a new United Nations report.
The UN Secretary-General’s Special Report on “Challenges related to sea-level rise and ways and approaches to address it”, submitted to the General Assembly on August 31, identifies Mumbai, Kolkata and Dhaka among South Asia’s low-lying cities where sea-level rise could lead to large-scale displacement.
“In the low-lying deltas of South Asia, in cities such as Kolkata and Mumbai in India, and Dhaka, the defining impact is human displacement,” the report says. It estimates that more than 14 million people across these vulnerable areas are at immediate risk of losing their homes to permanent inundation.
For Mumbai, the threat is amplified by its geography and the sinking of land in some areas. Land subsidence can increase the relative impact of sea-level rise, while higher seas can worsen tidal flooding and storm-surge impacts.
The UN report also warns of saltwater intrusion, which can contaminate freshwater aquifers and coastal wells. Rising seas and storm surges could place additional pressure on Mumbai’s sanitation, housing, transport networks and other critical infrastructure.
The global trend behind the warning is accelerating. The report says global sea levels rose by 5.9 mm in 2024, compared with an average annual increase of 4.7 mm between 2014 and 2023.
Even under aggressive emissions-reduction scenarios, global sea levels are projected to rise by at least 0.5 metres by 2100. Under a worst-case scenario involving instability of the West Antarctic ice sheet, the rise could reach up to two metres, potentially turning extreme sea-level events into annual occurrences in vulnerable coastal areas.
Sea-level rise is only one part of Mumbai’s growing climate risk. BMC rainfall data indicates that the average rainfall recorded during very heavy rainfall events has increased from 132 mm to 182 mm over the past six years.
The city recorded 28 spells of very heavy rainfall lasting four hours or more over the last decade. Despite a forecast of below-normal rainfall this year, Mumbai saw three instances of more than 100 mm of rainfall within 24 hours during the first eight days of July.
Heavy rain coinciding with high tides can make it harder for stormwater to drain into the sea, increasing the potential for urban flooding.
The UN warning echoes concerns outlined in Mumbai’s Climate Action Plan (MCAP), released by the Brihanmumbai Municipal Corporation in 2021. The plan projected that 80% of Mumbai’s island city could be submerged by 2050 and estimated sea-level rise of 0.1 to 0.3 metres along Mumbai and 11 other Indian coastal cities over the following three decades.
Globally, around 770 million people live in coastal areas less than five metres above the high-tide line.
For Mumbai, the latest UN assessment underlines the need for faster coastal adaptation, resilient infrastructure and long-term planning as the city confronts a future of rising seas, sinking land and increasingly intense rainfall.
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