3.5 - Migration, global hubs and megacities

Why megacities grow

Large cities grow through both migration and the excess of births over deaths, so visible expansion cannot be attributed to migrants alone.

Rural–urban migration moves people from countryside to towns and cities within a country. A rural push factor makes staying less attractive: insecure agricultural income, mechanisation reducing labour demand, limited further education or damaged harvests. An urban pull factor makes moving attractive: varied employment, colleges, hospitals and existing family contacts. A potential migrant weighs expected wages against rent, transport, recruitment costs and risk. A city can attract people even when many jobs are informal because its opportunities appear better than the available alternatives. Information from earlier migrants lowers uncertainty and supports chain migration.

Natural increase means births exceed deaths. A large young adult population can produce many births even as fertility falls. Better sanitation and healthcare reduce mortality. Migrants who later have children contribute to natural increase, but counting the births again as migration would double-count growth. The population balance is births minus deaths plus arrivals minus departures, with boundary changes treated separately.

Mumbai, on India's west coast, combines port, manufacturing, business and entertainment activities. MMRDA's Census 2011 table gives Greater Mumbai approximately 12.44 million residents; this is a dated municipal figure, not a current estimate or the population of the wider metropolitan region. It already exceeds the ten-million threshold. Employment and service concentration help explain its attraction, but a population total alone cannot establish how much growth came from migration. MMRDA Census 2011 boundary table.

Growth and urban pressures

Urban growth creates problems when housing and infrastructure expand more slowly than demand, especially where low incomes restrict access to formal services.

In Mumbai, limited affordable land near employment can encourage dense informal housing and long commutes. The municipal Climate Action Plan (2022) identifies inadequate water connections in informal settlements, clogged open drains and high runoff where permeable space is limited. This is evidence of uneven service access and environmental pressure, rather than a measure of how much migration caused them. Mumbai Climate Action Plan, 2022. Informal settlements can support livelihoods and strong social networks, yet insecure tenure, overcrowding and inadequate drainage increase vulnerability. Do not equate informal housing with an absence of enterprise or blame its residents for a shortage of serviced land.

The causal sequence matters. More households raise demand for water; incomplete networks encourage costly private supply or unsafe sources; contaminated water then increases disease risk. More sewage without treatment damages rivers and coastal water. Road congestion and fuel combustion increase exposure to air pollution. Building on floodplains or replacing permeable ground with buildings increases runoff, while blocked drains make monsoon flooding harder to manage. Housing location therefore connects social inequality to environmental risk.

These effects depend on planning and investment. Dense development can make public transport and piped services efficient per person if they are provided. Upgrading drainage and tenure may reduce vulnerability without removing livelihoods. Relocation to distant housing can improve a building while worsening access to work. A judgement about urban growth must ask whose living conditions change and over what timescale.

Global hubs and interdependence

Global hubs attract international migrants because their firms and services connect to markets, investment and expertise across borders.

London and Singapore attract high-wage professionals in finance, technology and specialist services. TNC offices require skills and connections, while migrants gain wages, experience and career opportunities. London's Census 2021 recorded 40.6% of usual residents as born outside the UK. This measures a migrant stock accumulated over many years, including people who later gained citizenship; it is not a count of that year's arrivals. ONS, Census 2021.