Social Distancing has become the mantra of policy response to the 2020 Corona Outbreak. Economic forces have for centruries pushed people closer and closer together in urban agglomerations. The emergence of a major pandemic in the 21th century - although forewarned - obviously was not a risk factor considered seriously by these same economic forces - neither private nor public decisionmakers when promoting and allowing the construction of the great agglomerations.
Homo Sapiens where not made by nature to live in megacities. The corona outbreak is a piece of nature striking back as a reminder of the vulnerability of the artificial urban environment to the most basic of natural evolution - mutation of a virus.
Stier provides an empirical treatment of the relation between urban size and the speed of epidemic spread in the US during the 2020 corona outbreak. The main findings are:
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faster spreading in larger cities
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larger fractions of the population infected
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more aggresive distancing needed
The virus is new, i.e. everyone is susceptible. The virus provokes a respiratory disease which makes transmission easy. The reproductive number \(R_{eff}\) seems to be higher than for ordinary influenza. Two factors determine how contagious the disease is: 1)length of the infectious period and 2) social contact intensity. Cities are the best breeding ground due to the high contact intensity.
The higher socioeconomic connectivity of larger cities in a fast urbanizing world makes containing emergent epidemics harder. But the density of socioeconomic connections in cities can also facilitate the spread of information, social coordination, and innovations necessary to stop the spread of COVID-19. This information and associated actions can easily spread much faster than the biological viral contagion. To fight an exponential, we need to create an even faster exponential! (Stier 2020)
So - the fight between Humans and Nature goes on! The bigger question - of course - being whether Humans should consider stopping creating such large [unhuman] agglomerations. There are many diseconomics to scale - epidemics being just one. Cities grow due to dominant economics of scale -i.e. benefitting the rich and powerful. The diseconomics are borne by others. Changing the current path does not seem easy - it goes to the core issue of Capitalism. This is treated elsewhere. Here we return to the more narrow theme of Urban Scaling.
“Scaling laws are power-law relationships of the form \(Y = cX^β\), where \(Y\) represents a variable which varies in a systematic way with the size \(X\) of subsystems and \(c\) and \(β\) are parameters. They have two powerful advantages: they summarize structural features of systems in a very efficient way, and they reveal the effect of universal constraints acting on the structure and development over several orders of magnitude in these systems… The main resources enabling urban development are the technical and cultural innovations which increase the productivity, the diversity and the cohesion of human activities; the availability of these resources relies on the production and exchanges of information … The role of cities as centers for the integration of human capital and as incubators of invention was rediscovered by the “new” economic growth theory, which posits that knowledge spillovers among individuals and firms are the necessary underpinnings of growth (Lucas 1988, Romer 1986) … This seemingly spontaneous process, whereby knowledge produces growth and growth attracts knowledge, is the engine by which urban centers sustain their development through unfolding innovation. The essential role of knowledge generation, recombination and circulation within and across urban areas must be at the core of any proposed explanation for urban scaling.” (Pumain 2006)
Urban Scaling Research finds that Social Contact Intensity is linked to City Size approximately as a power law:
\[k(N) = k_{0} N^δ\]with \(δ \approx 1/6\)
Links:
Dyrehaugen Corona Outbreak Analysis
Bettencourt (2013) Origins of Scaling in Cities pdf
Keuschnigg (2019) Scaling Trjectories of Cities pdf
Lucas (1988) On the Mechanics of Economic Development pdf
Pumain (2006) Evolutionary Theory of Urban Scaling pdf
Romer (1986) Increasing Returns and Long-Run Growth pdf
Schläpfer (2014) Scaling of Human Interactions with City Size pdf
Stier (2020) COVID-19 attack rate increases with citysize pdf