Mumbai and Kolkata are under threat because of increasing water levels in the oceans, a new report by the United Nations has shown. Both Mumbai and Kolkata are among the South Asian cities that are low-lying and may be increasingly affected by floods and even inundations in the future.
It has also given rise to claims of a viral nature about how Mumbai and Kolkata would be submerged by 50% in 2033. However, the UN has not made any such claim. What the warning actually talks about is the effect of sea-level rise on people and infrastructure over a period of time.
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| Image Credit: The Indian Express (Amit Chakravarty) |
What the UN Says About Mumbai and Kolkata
The special report of the Secretary-General of the United Nations on the issue of sea level rise was released on August 31, 2026. The report focuses on the impacts of rising seas on coastal areas and actions by governments.
The report specifically draws attention to the Indian cities of Mumbai and Kolkata, along with the Bangladeshi city of Dhaka, as vulnerable South Asian low-lying cities that face the threat of forced migration.
According to the UN, more than 14 million people in these areas are at immediate risk of losing their homes to permanent inundation.
The phrase "permanent inundation" doesn’t imply that whole cities will be submerged in water instantly. Instead, this term means that there will be a permanent effect of water on land and residential areas, which will make them uninhabitable.
The UN also points out that Mumbai and Kolkata sea-level rise risks are made worse by land subsidence. When the ground sinks while sea levels continue to rise, coastal flooding can become more severe.
Why Are Mumbai and Kolkata at Risk?
Mumbai is a significant coastal metropolis with many inhabitants and considerable infrastructure near the coast. An increase in sea levels will raise the risk of flooding in the city, especially if there are storms and other severe weather conditions.
Mumbai also faces the problem of land subsidence and saltwater intrusion. Saltwater can enter freshwater sources and affect drinking water, groundwater, and other resources.
The city of Kolkata is threatened with the same issues due to its placement in the low-lying Ganges delta area. The location of the city makes it susceptible to the problems of flooding and rising levels of the sea in Kolkata. The issue does not end here but goes beyond houses and can affect other infrastructural components as well.
Sea Levels Are Rising Faster
The UN report says global sea levels rose by nearly 5.9 mm in 2024, the highest annual increase recorded. Between 2014 and 2023, the average annual rise was around 4.7 mm. Warming oceans and the melting of glaciers and ice sheets are major reasons behind rising sea levels.
The UN says the effects are already being felt in coastal areas around the world. Around 770 million people currently live in coastal areas less than five metres above the high-tide line and face significant risks. The problem has particular significance for India because many of its large cities and populous areas are situated on coastlines that are at risk.
Is Mumbai Going Underwater by 2033?
The viral claim that Mumbai will be 50% underwater by 2033 is not supported by the latest UN report. The report does not give 2033 as the year when Mumbai or Kolkata will be submerged. Instead, it discusses the increasing risks that could develop over the coming decades.
There are separate climate assessments about Mumbai's future flood risks. A previous Mumbai Climate Action Plan had warned about significant long-term risks to the city from sea-level rise and flooding. However, those projections should not be presented as a UN prediction that half of Mumbai or Kolkata will be underwater by 2033.
The actual concern is that rising sea levels in India could gradually increase flooding, displacement, and damage to coastal infrastructure if cities are unable to adapt.
What Can Be Done?
In regard to this problem, the UN has emphasised the necessity for improved adaptation efforts as well as international cooperation.
For cities like Mumbai and Kolkata, proper flood management, coastal protection, climate-proof infrastructure, and conservation of freshwater would likely become more significant. Reduction of greenhouse gases is also very crucial, as the degree to which sea levels will rise in the future is dependent on the extent of global warming mitigation.
Conclusion
The latest warning from the UN has refocused on the rise in sea levels in Mumbai-Kolkata and the dangers that Indian coastal cities are facing.
More than 14 million people across low-lying areas, including Mumbai and Kolkata, could be at immediate risk of losing their homes to permanent inundation. However, this does not mean that Mumbai and Kolkata will be 50% underwater by 2033.
The real warning is about a gradual increase in flooding, displacement, and coastal risks. Preparing cities today could help reduce the impact of Mumbai sea-level rise and Kolkata flooding in the future.
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Author - Saurabh