10 Coastal Cities at Risk of Being Underwater by 2100: Rising Seas Threaten Millions

Rising sea levels have accelerated over the past century, averaging 0.20 meters from 1901 to 2023, with rates of 3.7 mm per year and ongoing acceleration. Melting ice sheets in Greenland and Antarctica, along with ocean warming, contribute to thermal expansion, increasing the risk to coastal cities.

Many urban centers already experience subsidence, worsening the impact of rising oceans. Cities like Jakarta, Miami, and Shanghai face compound threats from sinking land, storm surges, and high tides, placing millions of residents and trillions in assets at risk. As extreme flooding events become more frequent, adaptation measures struggle to keep pace, highlighting the urgent need for resilient urban planning.

Rising Sea Levels: 10 Climate Risk Cities

Rising sea levels are accelerating, putting millions of people and trillions in assets at risk across coastal megacities. Factors like land subsidence, storm surges, and high tides amplify flooding threats, especially in densely populated deltas and barrier islands. Scientists warn that without significant adaptation, many of the world's largest cities could face frequent or permanent inundation by 2100.

• Jakarta, Indonesia: Sinking 25 cm per decade, with 80% of the capital below sea level. Relocation plans are underway, but 10 million residents remain exposed to flooding.
• Miami, USA: Subsidence at 9 mm per year and barrier islands just 2 meters above sea level face storm surges up to 6 meters. The city holds $400 billion in assets at risk.
• Shanghai, China: With 26 mm annual subsidence, the 30-million-strong metro area sits on a 4-meter elevation. Existing sea walls and the Three Gorges Dam are insufficient for projected 2-meter sea-level rise.
• New Orleans, USA: Positioned 1.8 meters below sea level, levee systems are constantly tested by hurricanes. The city faces an annualized 1-in-1000-year flood threat.
• Dhaka, Bangladesh: At 4 meters elevation, 80% of the population experiences annual flooding. Ganges Delta subsidence amplifies risks for 20 million residents.
• Alexandria, Egypt: Nile Delta subsidence of 3 mm per year threatens UNESCO heritage sites and 5 million residents. Coastal inundation risk is significant for 40% of the city.
• Guangzhou, China: Pearl River Delta city sits at 6 meters elevation, with 15 million residents. Typhoon intensity and storm surges could flood 20% of the area.
• Ho Chi Minh City, Vietnam: Mekong Delta subsidence and 1.1-meter relative sea-level rise could displace 7 million residents. Flooded areas already cover 20% of the city.
• Karachi, Pakistan: At 8 meters elevation, glacier melt and Indus Delta changes threaten 20 million residents. By 2060, submersion projections could affect over a third of the city.
• Mumbai, India: With 14 meters elevation, subsidence, mangrove loss, and heavy monsoon rainfall threaten 21 million residents. Coastal flooding is increasingly severe.

These climate risk cities highlight the global scale of rising sea levels and the compounding impact of subsidence on vulnerable populations.

Climate Risk Cities: Subsidence and Compounding Sea Level Rise

Subsidence intensifies flooding risks, with groundwater extraction and urban weight causing irreversible sinking in many megacities. Jakarta alone loses 40 cm per decade, surpassing absolute sea-level rise. Combined with global sea-level increases of 3–6 mm per year, subsidence often dictates vulnerability more than ocean rise itself.

Adaptation strategies such as dikes, pumping stations, and barrier islands are effective in some regions but cost-prohibitive for developing nations. Cities face economic impacts exceeding $14 trillion annually under high-emission scenarios, with insurance markets struggling to cover escalating damages. Integrated land use planning, coastal defenses, and socioeconomic transformation are critical to mitigate rising risks.

Coastal Flooding: Storm Surges and Adaptation Limits

Storm surges are amplified by rising sea levels, warmer oceans, and high-pressure weather systems. High-emission scenarios could raise sea levels 0.63–2.1 meters by 2100, turning 1-in-100-year floods into annual events in some regions. Cities like Miami and Jakarta face large-scale permanent inundation without significant intervention.

Adaptation measures include managed retreat, floating infrastructure, and nature-based solutions such as mangrove restoration. Yet these strategies are often limited by cost, space, or governance challenges. The urgency of action is clear as both population exposure and asset vulnerability continue to grow, emphasizing the need for resilient urban planning.

Rising Sea Levels 2100: Preparing for Coastal Futures

The 10 climate risk cities illustrate how rising seas, subsidence, and storm surges interact to threaten urban life. Without proactive adaptation, millions may be displaced, and trillions in assets could be lost.

Innovative solutions, from sea walls to amphibious housing, must be coupled with policy, planning, and community engagement. Preparing for these scenarios requires global cooperation, investment in sustainable infrastructure, and early action to reduce emissions and enhance resilience in vulnerable cities.

Frequently Asked Questions

1. Which cities are most at risk from rising sea levels?

Jakarta, Miami, and Shanghai are among the most vulnerable due to low elevation, rapid subsidence, and high population density. Other cities like New Orleans, Dhaka, and Ho Chi Minh City face similar threats. Coastal infrastructure and storm surge protection are often insufficient. These areas may experience flooding more frequently as sea levels rise.

2. How does subsidence affect coastal flooding?

Subsidence worsens the impact of sea-level rise by lowering the land surface. Groundwater extraction and urban development accelerate sinking. Cities experiencing both subsidence and ocean rise face higher flood risks. Adaptive measures like pumps or barriers are necessary but may be costly or unsustainable.

3. What adaptation strategies can cities use to combat sea-level rise?

Cities can build seawalls, improve drainage, restore mangroves, or create floating infrastructure. Managed retreat and buyouts relocate vulnerable populations. Urban planning can integrate flood zones and resilient construction. Early investment in these strategies reduces long-term economic and human costs.

4. How many people could be displaced by 2100 due to rising seas?

Projections suggest up to 200 million people may be displaced under high-emission scenarios. Large populations in low-lying deltas are especially vulnerable. Displacement may occur gradually or suddenly during extreme storm events. Effective adaptation can mitigate the scale of forced migration.