UN Warns Mumbai, Kolkata, Dhaka Face Permanent Inundation Risk by 2100

04 Sep UN Warns Mumbai, Kolkata, Dhaka Face Permanent Inundation Risk by 2100

✎ Sea level rise is accelerating due to global warming, with coastal megacities like Mumbai facing compounded risks from land subsidence, saltwater intrusion, and storm surges, necessitating urgent climate adaptation and disaster…

Subject Relevance — Where This Topic Fits

• GS Paper I — Geography: Physical and Human Geography — Climate Change and Associated Hazards  |  GS Paper III — Environment and Ecology — Climate Change and Disaster Management  |  GS Paper III — Environment and Ecology — Urbanisation and its Challenges  |  GS Paper III — Environment and Ecology — Conservation, Environmental Pollution and Degradation
• Prelims: Sea level rise, Storm surges, Land subsidence, Saltwater intrusion, Climate Action Plan, Disaster resilience, Coastal vulnerability, IPCC projections
• Essay: Climate change and human displacement: A global challenge, Urban resilience in the face of environmental degradation

Quick Revision: Sea level rise is accelerating due to global warming, with coastal megacities like Mumbai facing compounded risks from land subsidence, saltwater intrusion, and storm surges, necessitating urgent climate adaptation and disaster risk reduction strategies.

Why is this in the news?

A United Nations report submitted on August 31 has flagged Mumbai, Kolkata, and Dhaka as among the South Asian megacities facing severe risks of permanent inundation due to accelerating sea level rise. For Mumbai, compounded risks from land subsidence, saltwater intrusion, and storm surges threaten critical infrastructure, freshwater resources, and human settlements, necessitating urgent climate adaptation and disaster risk reduction measures.

Background

• Coastal megacities in South Asia, including Mumbai, are particularly vulnerable due to their high population density, rapid urbanisation, and low-lying deltaic geographies.
• Land subsidence in Mumbai, exacerbated by groundwater extraction and urban development, intensifies the impact of sea level rise by lowering the elevation of coastal areas.
• The Brihanmumbai Municipal Corporation (BMC) released the Mumbai Climate Action Plan (MCAP) in 2021, which projected that 80% of Mumbai’s island city could be submerged by 2050 under high-emission scenarios.
• Historical data indicates a rise in extreme rainfall events in Mumbai, with average rainfall during very heavy rainfall events increasing from 132 mm to 182 mm over the past six years, further exacerbating flood risks.
• The Arabian Sea has shown signs of warming, contributing to changes in sea surface temperatures and intensifying extreme weather events, including storm surges and cyclones.

Understanding Sea Level Rise and Its Impacts on Coastal Megacities

• Sea level rise is primarily driven by two mechanisms: thermal expansion of seawater due to ocean warming and the addition of meltwater from glaciers, ice caps, and ice sheets, particularly in Greenland and Antarctica.
• Coastal megacities such as Mumbai, Kolkata, and Dhaka are at heightened risk due to their low-lying deltaic geographies, high population density, and exposure to storm surges and extreme rainfall events.
• Land subsidence, caused by excessive groundwater extraction, urban construction, and natural geological processes, exacerbates the impact of sea level rise by reducing the elevation of coastal areas relative to sea level.
• Saltwater intrusion occurs when rising sea levels push saline water into freshwater aquifers and coastal wells, contaminating drinking water sources and agricultural land.
• Storm surges, driven by cyclones and high tides, can overwhelm coastal defences, leading to flooding of low-lying areas, damage to infrastructure, and displacement of populations.
• The Mumbai Climate Action Plan (MCAP) 2021, prepared by the Brihanmumbai Municipal Corporation, projects that 80% of Mumbai’s island city could be submerged by 2050 under high-emission scenarios, highlighting the urgency of adaptation measures.

Key Features

Feature	Significance
Global sea-level rise	Accelerated by climate change, with a record 5.9 mm annual increase in 2024; projected to reach 0.5–2 metres by 2100, threatening coastal megacities.
Land subsidence in Mumbai	Geological sinking of land exacerbates flooding risks, compounding the impact of rising sea levels on infrastructure and groundwater.
Saltwater intrusion	Infiltration of seawater into freshwater aquifers and coastal wells, compromising potable water supplies and agricultural productivity.
Storm surges	Extreme weather events driven by warming oceans intensify coastal flooding, straining sanitation, housing, and transport systems.
Changing rainfall patterns	Increased frequency and intensity of heavy rainfall events in Mumbai, as evidenced by BMC data (e.g., 182 mm in very heavy rainfall vs. 132 mm previously).

Why it Matters

Environmental Sustainability

• Urgent need for climate adaptation strategies to mitigate displacement risks for over 14 million people in South Asian megacities, including Mumbai, Kolkata, and Dhaka.
• Intergenerational equity concerns arise from irreversible sea-level rise, necessitating long-term policy frameworks beyond electoral cycles.
• Biodiversity loss in coastal ecosystems due to saltwater intrusion and habitat degradation, affecting fisheries and livelihoods.

Urban Governance and Infrastructure

• Critical evaluation of Mumbai’s Climate Action Plan (MCAP, 2021) projections, which warn of 80% submergence of the island city by 2050 under high-emission scenarios.
• Infrastructure resilience challenges, including sanitation systems, housing, and transport networks, requiring retrofitting and climate-proofing investments.
• Public health risks from waterborne diseases due to flooding and contaminated water sources, necessitating integrated disaster management plans.

Economic Implications

• Potential GDP losses from climate-induced displacement, infrastructure damage, and operational disruptions in Mumbai’s financial and trade hubs.
• Insurance and financial sector exposure to climate risks, including underwriting challenges for properties in flood-prone zones.
• Impact on informal economies reliant on coastal activities, such as fishing and tourism, which may face displacement or reduced productivity.

Geopolitical and Regional Stability

• Cross-border implications of mass displacement in South Asia, where climate-induced migration could strain resources and social cohesion in neighboring countries.
• Need for international cooperation on climate financing, technology transfer, and adaptation strategies to address shared vulnerabilities.

Challenges

1. Climate-Induced Displacement

• Risk of permanent inundation displacing over 14 million people in South Asian megacities, with Mumbai facing compounded risks from land subsidence and saltwater intrusion.
• Social and humanitarian challenges in resettling displaced populations, including access to housing, livelihoods, and basic services.
• Legal and ethical dilemmas in defining climate refugees and establishing frameworks for their protection and rehabilitation.

UPSC Link: GS III: Disaster Management

2. Infrastructure Vulnerability

• Critical infrastructure in Mumbai, including sanitation, housing, and transport systems, is highly susceptible to storm surges and flooding.
• Retrofitting existing infrastructure to withstand climate impacts requires substantial financial and technical resources.
• Urban planning must integrate climate resilience into zoning laws, building codes, and land-use policies.

UPSC Link: GS III: Infrastructure

3. Water Security and Groundwater Depletion

• Saltwater intrusion into aquifers threatens Mumbai’s freshwater supply, exacerbating water scarcity in a city already facing high demand.
• Over-extraction of groundwater for urban and industrial use accelerates land subsidence, compounding flooding risks.
• Need for integrated water resource management, including rainwater harvesting, desalination, and aquifer recharge initiatives.

UPSC Link: GS III: Water Resources

4. Extreme Weather Events

• Increasing frequency and intensity of heavy rainfall events in Mumbai, as evidenced by BMC data, intensify urban flooding risks.
• Warming of the Arabian Sea contributes to changes in sea surface temperatures, amplifying extreme rainfall and heat events.
• Limited capacity of urban drainage systems to handle sudden deluges, necessitating green infrastructure and floodplain restoration.

UPSC Link: GS III: Climate Change

5. Policy and Governance Gaps

• Discrepancies between global climate projections and local adaptation policies, such as the MCAP’s submergence warnings versus current infrastructure resilience.
• Need for multi-stakeholder coordination among municipal, state, and central governments to implement climate action plans effectively.
• Lack of standardized methodologies for climate-risk assessments that account for human displacement and social impacts.

UPSC Link: GS II: Governance

Challenges — UPSC Perspective

Issue	Concern
Sea-level rise	Irreversible inundation of coastal areas, threatening human settlements and ecosystems.
Land subsidence	Geological sinking of land exacerbates flooding risks in low-lying urban areas like Mumbai.
Saltwater intrusion	Contamination of freshwater aquifers reduces potable water availability and agricultural productivity.
Storm surges	Extreme weather events overwhelm urban infrastructure, leading to sanitation and housing crises.
Changing rainfall patterns	Increased intensity and frequency of heavy rainfall events strain urban drainage systems.
Policy fragmentation	Lack of integrated climate adaptation strategies across municipal, state, and national levels.

Way Forward

• Enhance climate-risk assessments for Mumbai using high-resolution data on sea-level rise, land subsidence, and extreme weather events to inform urban planning.
• Invest in green and blue infrastructure, such as mangrove restoration and permeable pavements, to mitigate flooding and saltwater intrusion.
• Develop comprehensive resettlement and rehabilitation policies for communities at risk of displacement, ensuring access to housing, livelihoods, and basic services.
• Strengthen Mumbai’s Climate Action Plan (MCAP) with time-bound targets for reducing greenhouse gas emissions and retrofitting critical infrastructure.
• Promote integrated water resource management through rainwater harvesting, desalination, and aquifer recharge to address groundwater depletion and saltwater intrusion.
• Foster regional cooperation with neighboring countries (e.g., Bangladesh) to address shared climate risks and displacement challenges.
• Improve early warning systems and disaster response mechanisms to mitigate the impact of storm surges and extreme rainfall events.

UPSC Value Addition

Prelims Practice Questions

Q1. Consider the following statements regarding the UN report on sea-level rise:
1. The report projects at least 0.5 metres of global sea-level rise by 2100 under aggressive emissions reduction scenarios.
2. The report identifies Mumbai, Kolkata, and Dhaka as cities at immediate risk of permanent inundation.
3. The report does not consider land subsidence or saltwater intrusion as contributing factors to coastal vulnerability.
How many of the above statements are correct?

1. Only one
2. Only two
3. All three
4. None

Answer: Only two — Statement 1 is correct as the report projects a minimum of 0.5 metres sea-level rise by 2100 under aggressive emissions reduction. Statement 2 is correct as these cities are explicitly mentioned. Statement 3 is incorrect as the report acknowledges land subsidence and saltwater intrusion as compounding risks.

Q2. Assertion (A): Mumbai’s Climate Action Plan (MCAP) 2021 projects that 80% of Mumbai’s island city could be submerged by 2050.
Reason (R): The MCAP attributes this risk primarily to increased industrial activity and urban sprawl rather than climate-induced sea-level rise.
Options:
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.

Answer: ? — Assertion (A) is true as the MCAP does project 80% submergence by 2050 due to sea-level rise. Reason (R) is false because the MCAP attributes the risk to climate-induced sea-level rise, not industrial activity.

Q3. Match the following pairs related to climate-induced risks in coastal cities:
Column I (City) Column II (Risk Factor)
1. Mumbai a. Saltwater intrusion into freshwater aquifers
2. Kolkata b. Storm surges affecting sanitation infrastructure
3. Dhaka c. Land subsidence exacerbating inundation
Options for matching:
A. 1-a, 2-b, 3-c
B. 1-c, 2-a, 3-b
C. 1-b, 2-c, 3-a
D. 1-a, 2-c, 3-b

Answer: ? — Mumbai faces saltwater intrusion (1-a), Kolkata is vulnerable to storm surges (2-b), and Dhaka is affected by land subsidence (3-c).

Mains Practice Question

✍ The United Nations has warned that rising sea levels pose an existential threat to South Asian megacities like Mumbai, Kolkata, and Dhaka, with potential large-scale human displacement. Critically analyse the governance and policy challenges in mitigating these risks, with reference to India’s institutional framework and recent climate action plans. (15 Marks)

Approach: MODEL-ANSWER SKELETON:
1. **Context and Data**: Reference the UN report’s projections (0.5 m to 2 m sea-level rise by 2100), Mumbai’s Climate Action Plan (MCAP 2021) projections (80% submergence by 2050), and compounding factors (land subsidence, saltwater intrusion, storm surges).

2. **Governance Framework**:
– **Institutional Roles**: Role of the National Disaster Management Authority (NDMA), Ministry of Environment, Forest and Climate Change (MoEFCC), and state-level bodies like the Brihanmumbai Municipal Corporation (BMC).
– **Legal Provisions**: Reference the Disaster Management Act, 2005; National Action Plan on Climate Change (NAPCC); and state climate action plans.
– **Policy Instruments**: National Adaptation Fund for Climate Change (NAFCC), Climate Smart Cities Assessment Framework (CSCAF), and urban resilience strategies.

3. **Challenges**:
– **Institutional Fragmentation**: Overlapping mandates between central, state, and local bodies.
– **Resource Constraints**: Limited funding for adaptation measures (e.g., mangrove restoration, seawalls, drainage systems).
– **Urban Planning Gaps**: Lack of integration of climate risk assessments in city master plans.
– **Technological and Data Limitations**: Inadequate high-resolution coastal mapping and early warning systems.

4. **Recent Initiatives**:
– **Mumbai’s Climate Action Plan (MCAP 2021)**: Focus on coastal protection, drainage improvement, and freshwater management.
– **National Adaptation Plan (NAP)**: Emphasis on coastal zone management and livelihood diversification.

5. **Comparative Perspective**: Contrast India’s approach with global best practices (e.g., Netherlands’ Delta Programme, Bangladesh’s Climate Resilient Participatory Afforestation and Reforestation Programme).

6. **Way Forward**:
– Strengthen multi-level governance (central-state-local coordination).
– Invest in nature-based solutions (mangroves, wetlands) and grey infrastructure (seawalls, stormwater drains).
– Enhance community-based adaptation and early warning systems.
– Integrate climate risk assessments into urban planning and infrastructure development.

7. **Conclusion**: Emphasise the urgency of adaptive governance to address irreversible displacement risks, balancing mitigation and adaptation under SDG 13.

Source: The Indian Express

Maharashtra PCS (MPSC) — State PCS Practice

Prelims: According to the UN report, which of the following factors is NOT cited as a major contributor to Mumbai’s risk of permanent inundation?

1. Rising sea levels due to climate change
2. Unplanned urbanization and coastal encroachments
3. Inadequate drainage and sewage infrastructure
4. Increased frequency of cyclones in the Arabian Sea

Answer: Increased frequency of cyclones in the Arabian Sea — The UN report highlights sea-level rise, unplanned urbanization, and inadequate infrastructure as key risks, but does not specifically emphasize cyclones in the Arabian Sea as a major factor for Mumbai’s inundation.

Mains: Analyze the socio-economic and environmental implications of Mumbai’s potential permanent inundation as flagged by the UN. Suggest a multi-stakeholder strategy to mitigate these risks while ensuring sustainable urban development in Maharashtra.

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