Climate Change and Displacement Patterns

2.1 Climate Drivers of Migration

Climate change drives population movement through several pathways. These drivers rarely act alone; they overlap, and they can be divided into slow-onset change and sudden-onset disasters. When several environmental stresses combine, they can trigger displacement cascades in which initial environmental change leads to economic collapse, which drives migration and in turn puts pressure on destination areas.

Classification of Climate Migration Drivers

┌────────────────────────────────────────────────┐
│             Climate Migration Drivers          │
└──────────┬──────────────────────────┬──────────┘
           │                          │
  ┌────────▼─────────┐       ┌────────▼────────┐
  │   Slow-onset     │       │  Rapid-onset    │
  └────────┬─────────┘       └────────┬────────┘
           │                          │
  • Sea level rise             • Typhoons/hurricanes
  • Desertification/drought    • Floods
  • Glacial melt               • Wildfires
  • Soil erosion, salinity     • Heatwaves

        ┌──────────────────────────────┐
        │  Compound impacts            │
        │  • Threats to food security  │
        │  • Water scarcity            │
        │  • Loss of livelihoods       │
        │  • Health risks              │
        │  • Social conflict           │
        └──────────────────────────────┘
            

2.1.1 Slow-onset Drivers

Slow-onset climate change unfolds over years to decades and gradually pushes people to leave. Because it is gradual, it is poorly captured in displacement statistics.

2.1.2 Rapid-onset Drivers

Extreme weather events cause large-scale displacement within a short time and, when repeated, deny communities time to recover between events. Since 2008, weather-related disasters have displaced about 21.5 million people per year on average (UNHCR, based on IDMC data).

2.2 Regional Vulnerability Analysis

The impacts of climate change are not evenly distributed. Some regions are particularly vulnerable because of geographic, economic and social factors. The map below is a qualitative overview; the ratings are this book's relative assessment.

Global Climate Displacement Vulnerability Overview (qualitative)

Very high ████   High ███   Medium ██

North America  Alaska ███ (permafrost thaw)
               Caribbean ████ (hurricanes, sea level rise)
               Central American Dry Corridor ███ (drought)
South America  Andes ███ (glacial melt)
               Northeast Brazil ███ (drought)
Europe         Mediterranean coast ██ (heat, wildfire)
               Netherlands ██ (sea level rise, high adaptive capacity)
Africa         Sahel ████ (drought, conflict)
               Horn of Africa ████ (drought, food crisis)
               Nile Delta ███ (sea level rise)
               Mozambique ████ (cyclones, floods)
Asia           Bangladesh ████ (floods, cyclones, sea level rise)
               Himalaya ███ (glacial melt)
               Philippines ████ (typhoons)
               Mekong Delta ████ (sea level rise, subsidence)
               Central Asia ███ (drought, water scarcity)
Oceania        Tuvalu, Kiribati, Marshall Islands ████ (sea level rise)
               Fiji ███ (cyclones, sea level rise)
            

2.2.1 Asia-Pacific

2.2.2 Bangladesh: On the Front Line of Climate Displacement

Bangladesh is regarded as one of the countries most vulnerable to climate change. Most of its territory lies in the low-lying Ganges-Brahmaputra-Meghna delta, and its population density is very high.

2.2.3 Pacific Island States: Nations at Risk of Losing Territory

Together these four countries have about 700,000 people. The risks they face extend to the continued existence of national territory and to statelessness, which are discussed in Chapter 3.

2.2.4 Africa

2.2.5 The Sahel and the Horn of Africa

The Sahel is the semi-arid belt south of the Sahara, where highly variable rainfall, rising temperatures, conflict and weak governance overlap. Rainfall has partly recovered in places since the great droughts of the 1970s-1980s, but variability remains high, and climate factors combine with conflict and poverty to shape migration.

2.3 Impacts of Sea Level Rise

Sea level rise is one of the most visible and least reversible impacts of climate change; for some communities it can mean the permanent loss of territory itself.

2.3.1 Mechanism of Sea Level Rise

Causes of Sea Level Rise (contributions 1971-2018, IPCC AR6)

┌──────────────────────────────────────────────┐
│  Global warming (about +1.1°C in 2011-2020   │
│  relative to 1850-1900)                      │
└──────────────────────┬───────────────────────┘
          ┌────────────┼──────────────┐
          ▼            ▼              ▼
   ┌────────────┐ ┌────────────┐ ┌────────────┐
   │ Thermal    │ │ Glacier and│ │ Land water │
   │ expansion  │ │ ice-sheet  │ │ storage    │
   │ about 50%  │ │ loss ~42%  │ │ about 8%   │
   └─────┬──────┘ └─────┬──────┘ └─────┬──────┘
         └──────────────┼──────────────┘
                        ▼
              ┌───────────────────┐
              │  Sea level rise   │
              │  2006-2018:       │
              │  about 3.7 mm/yr  │
              └───────────────────┘
            

2.3.2 Secondary Impacts

Sea level rise does not just submerge land; it creates cascading effects that drive displacement even before areas become fully uninhabitable:

• Saltwater intrusion: contaminates fresh water and farmland, making areas hard to live in before they flood
• Increased storm surge: higher baseline sea levels let storms reach further inland
• Coastal erosion: accelerates land loss and damage to infrastructure and property
• Infrastructure failure: sewage, roads and water supply break down, making areas unlivable
• Economic collapse: falling property values and withdrawal of insurance trigger economic displacement

2.3.3 Major Coastal Cities and Deltas

Large low-lying cities and deltas face growing risk as sea level rise, storm surge and land subsidence combine. Hallegatte et al. (2013, Nature Climate Change) estimated that average annual flood losses in the world's 136 largest coastal cities could rise from about US$6 billion in 2005 to about US$52 billion by 2050 from socioeconomic change alone. Because city-level flooded areas and loss figures vary greatly with assumptions, the table below lists risk factors only.

2.4 Extreme Weather Events

Climate change is increasing the frequency and intensity of extreme weather, and repeated disasters leave no time for recovery, which is especially devastating for communities with limited resources.

2.4.1 Intensifying Typhoons and Hurricanes

2.4.2 Case Study: Displacement after Hurricane Katrina

2.5 Drought and Desertification

Because drought and desertification unfold slowly they receive less attention than sudden disasters, yet they affect agriculture, herding and water resources so widely that they can force whole communities to move.

Cascading Effects of Drought

        Initial drought
            │
            ▼
    ┌───────────────────┐
    │ Less rainfall     │
    │ Groundwater loss  │
    └───────┬───────────┘
    ┌───────┴────────┐
    ▼                ▼
┌───────────┐   ┌───────────┐
│ Crop      │   │ Livestock │
│ failure   │   │ losses    │
└────┬──────┘   └────┬──────┘
     └───────┬───────┘
             ▼
    ┌───────────────┐
    │ Food crisis   │
    │ Malnutrition  │
    └──────┬────────┘
           ▼
    ┌───────────────┐
    │ Lost income   │
    │ Social unrest │
    └──────┬────────┘
           ▼
    ┌───────────────┐
    │ Decision to   │
    │ migrate       │
    └───────────────┘
            

2.5.1 The Drought Displacement Pathway

1. Initial water stress: declining rainfall reduces agricultural productivity
2. Crop failures: repeated harvest failures destroy farming livelihoods
3. Livestock loss: pastoralists lose herds for lack of water and fodder
4. Economic hardship: loss of income, rising debt, asset depletion
5. Food insecurity: rising malnutrition, particularly among children
6. Health impacts: water-related disease, reduced access to health care
7. Social breakdown: rising tensions and resource conflicts
8. Migration decision: migration begins when adaptation options are exhausted
9. Rural-urban migration: initially to nearby cities
10. Cross-border movement: when domestic options fail

2.5.2 Major Drought-Risk Regions

2.6 Flooding and Water-Related Displacement

About 1.8 billion people worldwide are estimated to be directly exposed to 1-in-100-year floods (Rentschler et al., 2022, Nature Communications). Flooding takes several forms, each with a distinct displacement pattern.

2.6.1 Major Flood Displacement Regions

• Bangladesh: monsoon floods affect large parts of the country every year, and riverbank erosion causes permanent moves
• Pakistan: the 2022 floods affected about 33 million people (around 14% of the population) and displaced about 8 million
• Nigeria: recurrent flooding in the Niger and Benue basins (including the major floods of 2022)
• China: flooding in the Yangtze and Yellow River basins and rising urban flood risk
• Southeast Asia: flooding in the Mekong, Irrawaddy and Chao Phraya basins

2.7 Glacial Melt and Mountain Regions

Glaciers act as "water towers" supplying water, agriculture and hydropower to very large populations. As glaciers shrink, meltwater and the risk of glacial lake outbursts first increase, and later water supply declines.

Risk in Glacier-Dependent Regions

HINDU KUSH HIMALAYA (largest scale):
├─ About 240 million people in the mountains and about 1.65 billion
│  in downstream river basins (ICIMOD 2023)
├─ Major rivers: Ganges, Indus, Brahmaputra, Yangtze, Mekong and others
├─ Outlook: about 30-50% loss of glacier volume by 2100 at
│  1.5-2°C of warming (ICIMOD 2023)
└─ Displacement projections: highly uncertain; no robust global estimate

ANDES:
├─ Cities and rural areas dependent on tropical glaciers in Peru,
│  Bolivia, Ecuador and elsewhere
└─ Glacier retreat threatens dry-season water supply

CENTRAL ASIA:
├─ Tian Shan and Pamir glaciers feed the Amu Darya and Syr Darya
└─ High dependence on irrigated agriculture

ARCTIC:
├─ About 4 million people (Arctic Council)
├─ Permafrost thaw and coastal erosion destroy infrastructure
└─ Relocation of Indigenous villages under discussion, e.g. in Alaska
            

2.7.1 Phases of Glacial Melt

1. Increasing melt: more meltwater and glacial lake outburst risk; infrastructure damage and temporary displacement
2. Peak water: flow peaks and then begins to decline. Timing differs by basin; for many Hindu Kush Himalaya basins it is projected around mid-century
3. Decline: dry-season water shortages, more crop failures, rising migration pressure
4. Long-term scarcity: permanent migration pressure once adaptation limits are reached

2.8 Resource Conflicts and Migration

Climate change acts as a "threat multiplier" that intensifies competition over scarce resources such as water, land and food, producing conflict that in turn drives displacement.

The risk ratings above are this book's qualitative assessment; no robust quantitative estimates of future displacement by region are presented.

2.9 Migration Patterns and Trends

2.9.1 Distance and Direction of Movement

Main Movement Routes Where Climate Factors Play a Role
(including cases combined with other factors)

South Asia
    │  Rural Bangladesh → Dhaka and other cities
    │  Bangladesh → India (cross-border)
    │
Sub-Saharan Africa
    │  Rural Sahel → regional cities and neighbouring countries
    │  Horn of Africa → peri-urban settlements, neighbouring countries
    │
Latin America
    │  Central American Dry Corridor → cities → Mexico, United States
    │
Pacific island states
    │  Tuvalu → Australia (Falepili Union)
    │  Tuvalu, Kiribati, Tonga, Fiji → New Zealand (Pacific Access Category)
    │  Marshall Islands → United States (Compact of Free Association)
            

2.9.2 Temporal Outlook

Long-range displacement projections are highly uncertain because they depend on emission pathways, adaptation and development choices. The most widely cited modelling is the World Bank's Groundswell series (2018, 2021):

• By 2050: up to 216 million internal climate migrants across six world regions under a pessimistic scenario
• Hotspots: internal climate migration hotspots could emerge as early as 2030 and spread and intensify by 2050
• Room for action: immediate emission cuts combined with inclusive, resilient development could reduce the scale by as much as 80%

Cumulative projections beyond 2050 are not presented here because no robust estimate exists.

2.10 Conclusion

The relationship between climate change and migration is complex and multi-layered. Sea level rise, extreme weather, drought, flooding, glacial melt and resource conflicts operate on different timescales and move tens of millions of people every year. Asia-Pacific has the most disaster displacement, and Africa faces a serious crisis where drought and water scarcity overlap with conflict.

Understanding these patterns is essential for effective prevention, response and adaptation strategies. The next chapter examines the legal frameworks and rights that protect climate refugees.