How are megacities coping up after coronavirus?

London - High density ensured that once the virus had entered a megacity it would spread quickly and cause high death rates.

Densely-populated and highly-connected megacities such as London and New York have been the most dynamic centres of the modern economy but for the same reasons have proved especially vulnerable to the coronavirus.
Density and connectedness have supported a wealth of innovation and high productivity, but crowded housing, workspaces and transport systems have created ideal conditions for the transmission of pulmonary disease.
Regional, national and international connectedness ensured megacities were the first to receive the virus, and then transmitted it onward to secondary and tertiary cities and eventually rural areas.
High density ensured that once the virus had entered a megacity it would spread quickly and cause high death rates, forcing urban lockdowns to bring transmission back under control.
The coronavirus has intensified a pre-existing debate about the future of megacities, and whether the concentration of so much population and economic activity in a few large centres is desirable.
Long before the epidemic, analysts and policymakers had begun to question the distribution of activity between megacities and other primary cities on the one hand, and secondary and tertiary cities on the other.
Prior to the epidemic, the question was whether megacities had become too dominant, leaving other areas behind, and too unaffordable; now it is also whether they have become too unsafe and can recapture their past benefits.
Megacities still have advantages, but improvements in communications and the mass experiment in remote working have sharpened questions about whether some activity could relocate to secondary cities and other areas.
London
London is the quintessential megacity: Densely populated; intensely connected at regional, national and international levels; and exceptionally productive compared with other cities and regions in the United Kingdom.
London has more in common economically with other megacities - such as New York, San Francisco and the Bay Area, Tokyo, Sydney, Auckland, Paris, Beijing and Shanghai - than with most other parts of Britain.
Like other megacities, London's population has boomed over the last three decades, hitting a record of nine million in 2019, up from just 6.4 million in 1991, according to the UK Office for National Statistics.
However, before that, the city's population had slumped for five decades from a previous peak of 8.6 million in 1941, as inhabitants fled the city for more space and other improvements outside the metropolitan area.
Migration
Like other megacities, London's population shows exceptional levels of turnover compared with secondary cities and other non-metropolitan areas.
London is at the heart of two enormous circulations, exchanging population with other regions of the United Kingdom (especially adjacent regions in Southeast and East England), as well as internationally.
Every year, the British capital sees a large net outflow of adults aged 30 years and over to other regions of the country, which is partially replenished by a large net inflow of adults aged 20-29 years.
In the 12 months to June 2019, London saw a net outflow of almost 88,000 adults aged over 30, partially offset by a net inflow of 46,000 adults aged 20-29 from other regions.
London is the only major region of Britain that sees a net outflow of over-30s, and one of only two regions that see a net inflow of 20-29 year olds (the other being the Northwest), confirming the distinctiveness of its population and economy.
Overall, however, London has lost population to the rest of the country every year for the last decade, relying on international migration to replenish its population and achieve growth.
In the year to June 2018, London saw an outflow of 103,000 people to other regions of the United Kingdom, which was more than replaced by an inflow of 113,000 from other countries.
The city's net domestic outflow has been accelerating as it becomes more crowded and expensive, hitting a peak of 107,000 in 2016/17, up from 69,000 in 2013/14 and 32,000 in 2008-09.
Like other megacities, London is overwhelmingly young, relying on inward migration of the young from other regions and international recruitment to replace its loss of older inhabitants.
Young workers come from the rest of the country and overseas seeking better employment opportunities, while some older inhabitants leave seeking more affordable housing, more space and other lifestyle improvements.
London's population circulation is similar to other megacities such as New York, San Francisco, Auckland, Sydney and China's top-tier cities, including Wuhan where the pandemic began.
Population
The future population and economic activity of megacities depends on how coronavirus and other factors impact these massive inter-regional and inter-national migrations.
In the very short term, lasting perhaps a year, the epidemic is likely to lead to a fall in population in London and other megacities.
Health concerns and the desire for more space are likely to prompt accelerated outward migration, especially among older residents, while lack of job opportunities and curbs on international travel will temporarily curb inward migration.
In the medium and longer term, the question is whether megacities can restart their inward flow of migrants from other regions and countries to offset their older population losses.
In part, that will depend on the deployment of an effective vaccine and other control measures to reduce coronavirus transmission in densely populated areas.
But it also depends on whether megacities can resume attracting international migrants once travel restrictions are eased.
Britain's exit from the European Union, the developing US-China cold war, rising nationalism in many countries, and de-globalisation could make migration to megacities more restricted in future.
These cities will have to prove they continue to offer superior employment opportunities and incomes compared with other areas, enough to offset their substantially higher cost of living.
And they will have to maintain that benefit-cost advantage in an environment where central offices may play a smaller role and there is likely to be more remote working.
Finally, policymakers must also decide whether to try to reinforce the attractiveness of megacities, or exploit the epidemic to try, once again, to disperse more activity to secondary and tertiary centres.
Megacities generate enormous amounts of output, high-paying employment and tax revenues, but political cohesion favours a more even distribution of activity to other urban and semi-urban areas.
Policymakers in megacities, other regions and national level may have contrasting views on the desirability of any rebalancing of population and economic activity to other cities and regions.
London's population history over the last century shows the relentless growth of megacities is not inevitable or irreversible but contingent on their relative attractiveness to different age cohorts and openness to both inter-regional and inter-national migrants.