Bangladesh Faces 13.3 Million Internal Climate Migrants by 2050, ADB Warns

Rising seas and shrinking livelihoods threaten millions

Bangladesh could have 13.3 million internal climate migrants by 2050, about 7.5% of its population, as rising seas, water shortages and declining agricultural production push people to seek homes and work elsewhere, according to the Asian Development Bank (ADB). The warning puts a human figure on a widening coastal crisis, with the poorest households often facing the greatest danger and having the least money to recover.

The bank's Asia-Pacific Climate Report 2026, subtitled Coastal Risks on the Rise: Actions for a Resilient Future, examines 30 developing economies with coastlines. More than 400 million people live within 10 kilometres of their shores, in areas generating around $7 trillion in economic activity each year.

Bangladesh's exposure extends from homes and farms in its delta to the trade hubs of Chattogram and Mongla. Tidal surges, cyclones and salt entering soil and freshwater supplies can damage several foundations of daily life at once: shelter, drinking water, food production and earnings.

ADB projects sea levels across much of Asia and the Pacific will rise by 20 to 35 centimetres by 2050. Higher seas allow flooding to reach farther inland and make it harder for vulnerable communities to keep water and farmland usable. The report also identifies substantial returns from protection, estimating that investments in coastal resilience could deliver benefits worth about 20 times their cost.

Why losing a livelihood can mean leaving home

Bangladesh's migration risk comes from pressures that build on one another. A family may cope with a single flood, then face repeated crop losses, damaged housing and increasingly salty water. Moving becomes more likely when staying no longer provides a reliable living.

ADB finds that households facing the greatest coastal flood risk in Bangladesh, Myanmar and India also tend to have fewer resources to prepare, cope and recover. Savings, safer housing and access to services affect how quickly a family can resume work after a disaster.

Bangladesh also has a weak or uncertain version of the wealth advantage that coastal residents enjoy in several other countries studied by ADB. Across 10 countries, coastal households generally hold more assets than inland households, but that pattern is much less secure in Bangladesh and Myanmar. Living near an economically valuable coastline offers uneven protection against poverty.

The International Monetary Fund projects that rising seas could remove more than one seventh of Bangladesh's land area and nearly one third of its food production by 2050. Those prospective losses help explain why the migration challenge reaches beyond rebuilding houses: communities also need productive land, freshwater and dependable employment.

Three projections show the scale and uncertainty

ADB estimates 13.3 million internal climate migrants in Bangladesh by 2050; a World Bank projection puts the number as high as 19.9 million, while an academic model projects more than 22 million. Each estimate places substantial pressure on the communities people leave and those that receive them.

The climate migration study, published on May 9, 2025, in Frontiers in Climate, examines movement across 495 upazilas, local administrative areas. It combines climate projections with a computer simulation of how people might respond to flooding, heatwaves, cyclones and changing economic opportunities.

An agent based model represents people or households as simulated decision makers. In this study, climate data from the sixth Coupled Model Intercomparison Project, known as CMIP6, help estimate extreme weather risks, which then feed into possible decisions to move.

The simulation covers 2011 through 2050 and was run 10 times for each scenario. It uses 14,405 simulated agents, with roughly 15% to 16% migrating by the end of the period, translating into more than 22 million people nationally. The authors caution that their estimate may be high because the model has substantial limitations and both future climate conditions and human behaviour are uncertain.

The study projects much of the movement from central Bangladesh to other central and southeastern upazilas. Its findings give planners a reason to consider housing, employment and services across a wider area than the coastline alone.

Displacement is already part of daily life

Disasters triggered 14.7 million internal displacements in Bangladesh between 2014 and 2023, according to the Internal Displacement Monitoring Centre. The figure counts movements, so someone forced to leave home during several disasters can appear more than once.

Cyclone Amphan prompted the evacuation of 2.4 million people in Bangladesh in 2020 and killed 26. Evacuation provides immediate safety; the longer challenge begins when people return to damaged homes or discover that their land can no longer support them.

Dhaka already absorbs as many as 400,000 new migrants a year for a range of reasons, including employment. Climate pressures can add to that demand for accommodation, water, sanitation and jobs. The academic study's projected movement into other central and southeastern areas suggests that preparation also needs to extend beyond the capital.

Bangladesh's migration and climate milestones show how past disruption connects with future planning:

• 1985 to 2015: Coastal settlement across the region grew by 66.8%, while settlement exposed to flooding grew by 92.3%.
• 2014 to 2023: Disasters triggered 14.7 million internal displacements in Bangladesh.
• May 9, 2025: The academic study projecting more than 22 million internal climate migrants by 2050 was published.
• 2050: ADB projects 13.3 million internal climate migrants in Bangladesh and regional sea level rise of 20 to 35 centimetres.
• 2100: Regional coastal flood damage could reach about $739 billion annually under high emissions without adaptation.

Coastal development is putting more assets in danger

Asia and the Pacific are adding homes and infrastructure in places that face growing flood exposure. Between 1985 and 2015, settlement exposed to flooding expanded by 92.3%, compared with 66.8% for coastal settlement as a whole, a difference of 25.5 percentage points.

ADB estimates current annual coastal flood damage at about $27 billion. Without adaptation, that could rise to $172.4 billion by 2050 under an intermediate emissions pathway and $199.1 billion under a high emissions pathway. By 2100, the corresponding estimates reach $520.2 billion and $738.7 billion.

The intermediate pathway assumes emissions stay around current levels until the middle of the century before declining, with warming of approximately 2.7 degrees Celsius by 2100. The higher pathway involves continued heavy use of fossil fuels and warming approaching 4.4 degrees.

Under high emissions, more than 30 million people across the region could experience coastal flooding annually by 2050, rising to more than 100 million by 2100. In Bangkok, Jakarta, Kolkata and Mumbai, coastal floods historically expected about once in 100 years could occur annually by the century's end. A flood described as occurring once in 100 years has roughly a 1% chance of happening in any given year under the conditions used to calculate it.

Ports connect coastal hazards to inland incomes

Chattogram and Mongla face severe climate risks, making port resilience a concern for Bangladesh's wider economy. When a port closes or operates slowly, goods can be delayed between producers and customers, affecting businesses far from the shore.

ADB estimates that port disruptions put about $63 billion in global trade at risk annually. Asia and the Pacific account for $40 billion to $45 billion of that total, roughly two thirds to seven tenths of the global figure.

The Philippines illustrates how large future losses could become. Annual port losses there could reach $70.2 billion by 2100 under high emissions, equivalent to 0.44% of projected gross domestic product (GDP). Under moderate emissions, the estimate is $20.6 billion, or 0.19% of GDP.

Other projected annual port losses under high emissions include $54.3 billion in Indonesia, $36.2 billion in Vietnam, $35.6 billion in Malaysia, $32.6 billion in Thailand, $12.4 billion in Myanmar and $8.23 billion in Cambodia. These estimates cover repairs and rebuilding, revenue lost during shutdowns and disruption to maritime trade.

ADB describes why transport damage quickly becomes a household problem:

Because these networks link farms to markets, fishers to buyers, and households to health services and food supplies, their disruption cascades directly into livelihoods, nutrition, and well-being.

Bangladesh has protection to build on

Bangladesh has built about 5,000 multipurpose cyclone shelters, supported by early warning and evacuation systems. ADB presents this as an example of accommodation: changing buildings and activities so communities can live more safely with increasing hazards.

The report sets out four broad adaptation choices. Accommodation includes elevated buildings, better drainage, shelters and crops that tolerate salt. Protection uses seawalls, barriers, restored mangroves and other measures to defend existing settlements. Advancing creates raised land or infrastructure beyond the current shoreline. Retreat moves people and assets away from locations that become too dangerous.

Tuvalu provides an example of creating safer land, having developed 7.3 hectares of raised land in Funafuti designed to remain safe beyond 2100. Bangladesh's Delta Plan 2100 takes a broader approach to managing its delta, connecting water, agriculture, livelihoods, ecosystems and investment over time.

Local conditions determine which choices work. A dense port city may need progressively stronger protection, while rural communities may benefit from water management, restored ecosystems, changes in farming and gradual relocation where necessary. Moving a community also requires support for livelihoods and social connections, alongside a safer physical location.

Protection offers large returns, but funding falls short

ADB estimates that spending $9 billion to $19 billion annually on coastal flood protection throughout the century could avoid $178 billion to $360 billion in annual flood damage. The bank puts the regional benefits at about 20 times investment costs.

International public adaptation finance to coastal developing economies in Asia and the Pacific increased from about $5 billion in 2015 to an annual average of $11.4 billion in 2022 and 2023. Even after that increase, governments face large demands for sustained investment and maintenance.

ADB cites roughly $20 billion in annual resilience needs, based on costed adaptation plans from 15 coastal developing economies. Those plans use differing methods and time periods, cover wider adaptation needs, and exclude China and India. The bank therefore considers the estimate likely to understate the financing required.

Small island developing states face particularly heavy demands, with estimated adaptation needs equivalent to 2.4% to 3.9% of GDP. Under high emissions, annual coastal flood damage in atoll nations could reach 30% to 60% of GDP by 2100, putting an exceptionally large share of their economic output at risk.

ADB's review of 141 coastal resilience projects approved by the bank, the Green Climate Fund and the World Bank between 2010 and 2025 also finds uneven access to finance. Among countries outside the small island group, 71% of financing was concentrated in five countries.

Turning plans into lasting protection

Yevgeniy Zhukov, director general of ADB's Climate Change and Sustainable Development Department, has called for planning that considers risks over the long term and adjusts as conditions change. For Bangladesh, that means connecting decisions about settlements, ports, farming and water rather than treating each problem separately.

ADB recommends four priorities: make adaptive planning part of development decisions, strengthen institutions and governance, mobilise finance, and sustain implementation with local ownership. In practical terms, governments need to account for future flooding when approving development, coordinate agencies and maintain protection after construction ends.

Public budgets remain central because early warnings, flood defences and other shared services benefit entire communities. Ports, tourism, housing and some coastal industries can draw on a wider mix of public and private funding. Concessional finance, which offers more favourable terms than ordinary commercial lending, can help governments fund projects whose benefits build over decades.

Bangladesh's task reaches from protecting people during the next cyclone to preparing places that may receive migrants over the coming decades. The ADB projection gives that challenge a scale: 13.3 million people potentially moving within the country by 2050. Its investment findings also give governments a practical choice, with substantial future losses avoidable through sustained adaptation.

Key Points

• ADB projects 13.3 million internal climate migrants in Bangladesh by 2050, about 7.5% of its population.
• A World Bank projection reaches 19.9 million; an academic model projects more than 22 million, with substantial uncertainty.
• Disasters triggered 14.7 million internal displacements in Bangladesh between 2014 and 2023.
• Regional annual coastal flood damage could rise from about $27 billion today to $172 billion to $199 billion by 2050 without adaptation.
• Bangladesh has about 5,000 multipurpose cyclone shelters, while Chattogram and Mongla face severe climate risks.
• ADB estimates annual coastal protection investment of $9 billion to $19 billion could avoid $178 billion to $360 billion in annual flood damage.