3.2.4.4 - Migration processes and consequences

Categories, stocks and flows

Migration changes a person's usual place of residence; international migration crosses a national border, while internal migration stays within one country.

These broad distinctions follow UNHCR's definitions. Legal and regional definitions differ, so determine the applicable definition before interpreting a statistical category.

Economic migrants move chiefly for work or improved livelihood opportunities. Motives can overlap: a person fleeing violence may also seek employment, and livelihoods can be damaged by drought. An internally displaced person has been forced to move without crossing an international border. Environmental displacement does not automatically establish refugee status; the circumstances and applicable law matter. These categories describe different things—legal protection, location or motive—so they are not always mutually exclusive boxes.

A stock counts migrants resident in a destination at a specified date. A flow counts moves or people moving during an interval. Net migration is inward flow minus outward flow, using consistent definitions. A stock can change through arrivals, departures, deaths and changes in classification; it is not annual immigration.

UN DESA's International Migrant Stock 2024 estimates roughly 304 million international migrants at mid-2024. It chiefly uses foreign-born residents, with foreign citizenship as a proxy where needed. Japan's 2025 census foreign-nationality stock is a different date and definition, so subtracting it from a foreign-born estimate does not give a migration flow.

Causes become movement through processes

Environmental and socio-economic pressures become migration only where people have opportunities or are compelled to move.

Drought can reduce crops and income; flooding can destroy homes; longer-term sea-level rise can threaten habitability. These pressures interact with land tenure, safety nets, conflict and alternative jobs. A household may first adapt farming, send one member temporarily or move internally before an international move. The poorest may be unable to leave because journeys cost money: high exposure can produce immobility as well as migration.

Wage differences, education, family reunification, safety and services attract or compel moves. Recruitment agencies, transport, information and earlier migrants' networks reduce costs and uncertainty. Visa rules, border enforcement and qualification recognition can open or restrict routes. Smuggling and dangerous transit may arise where legal routes are limited, but migrants do not all share that experience.

For a flow map, identify origin, destination, time and arrow-width units. Width should represent a supplied flow, not an invented route or nationality stock. A map cannot reveal motives or experiences alone; interviews and administrative evidence add different information. Processes can include temporary work, circular moves, return, settlement and onward migration, so a single origin–destination arrow is a simplification.

In an original illustrative drought-affected village, one household sends an adult to a nearby city using relatives' contacts; another cannot afford transport. The same environmental shock creates different outcomes because resources and networks differ. This illustrates a mechanism without claiming observed fieldwork.

Demographic and economic consequences

Migration affects both population structure and economic activity, with gains and costs distributed unevenly.