Now the virus has hit the labour market and services. The result has been a narrative about residents leaving for secondary cities, towns and rural areas for more space and lower health risks. But the reality is more complicated.
Megacities have always been crowded, unhealthy places, susceptible to infectious disease. In the seventeenth and eighteenth centuries, London was so unhealthy more people died than were born in the city; the population only increased because of a steady inward migration from other parts of Britain.
The same was true of other disease-ridden and polluted historical megacities, including ancient Rome and early modern Naples, Paris, Calcutta, Bombay and Manchester. Constant inward migration offset extraordinarily high mortality rates that were much higher than in smaller towns and rural areas.
Modern megacities are healthier, though susceptible to epidemics. But they still rely on a steady inflow of younger migrants, domestic and international, to replace the outflow of older residents seeking cheaper accommodation.
London’s population increased by 1.5 million, or 21%, over the decade-and-a half to 2019, despite surging property prices and an increasingly overloaded transport system, as young workers and international migrants flooded in.
If the virus, and the possibility of other epidemic diseases in future, creates pressure for less density and crowding, however, megacities will have to offset that by becoming cheaper, at least for a time.
In low and middle-income countries, however, the urbanisation process is still at a relatively early stage, similar to the cities of Europe and North America in the nineteenth and early twentieth centuries.
Like their European and North American forerunners, the fast-growing megacities of Latin America, Africa and Asia will likely see continued population growth despite the epidemic.
The income and employment gap between megacities and other areas is wider, there are fewer opportunities for remote working, and the population structure is much younger.
The same pressures that drove migration to London, Paris, Manchester and New York between the eighteenth and early twentieth centuries, despite their health problems, will continue to drive urbanisation in emerging markets.
The epidemic is therefore likely to have the most profound impact on megacities and other primary urban centres in the OECD economies, with far less impact outside the OECD area.
Large primary cities can only be understood properly as part of a connected system with neighbouring regions, and in the case of global megacities with other countries.
In the case of London, the city has a constant outward migration of residents aged 30 years and older, which is replaced by an influx of new young residents and international migrants (https://tmsnrt.rs/3ipFMMx).
Between 2004/05 and 2018/19, London’s population increased by an average of 102,000 per year, according to the UK Office for National Statistics (“Local area migration indicators UK”, ONS, Aug. 17).
Over the period, the city’s population saw a natural increase of 77,000 per year, with net inward migration adding another 25,000 per year.
The city consistently lost population to other parts of Britain, with a net outflow every year. But this was more than offset by a net inflow from overseas, every year.
Other megacities exhibit similar migration systems, attracting young migrants and those from other domestic regions and internationally, while losing older residents to cheaper areas with more space and less crowding.
In the short term, the epidemic and its aftermath is likely to have an impact on both outflows and inflows from megacities in the advanced economies.
It is likely to sharpen concerns about health and crowding, while strengthening the desire for more space, which will likely accelerate the existing outflow of older residents.
At the same time, the downturn in economic activity and employment opportunities, as well as travel restrictions, is likely to slow the inflow of younger domestic and overseas migrants.
In the OECD, megacity populations are therefore likely to decline in the short term, or at least grow more slowly than before the epidemic.
Outside the OECD, the epidemic may have little impact because the urbanisation pressures are simply too strong.
Whether interruption to megacity population growth in the most advanced economies proves temporary or more durable depends on how quickly cities can restart inward migration of the young and international migrants to offset their loss of older residents.
Lifting international quarantine restrictions and resumption of international aviation will obviously be critical, so is a recovery in megacity employment markets for younger workers and social amenities.
But megacities may also need to become cheaper and more affordable for a time, relative to other regions, to attract more young inward migrants, and to reduce the opportunities for older residents to sell up and move out.
(Editing by Mark Potter)
© Reuters News 2020