In order to get substantial change in the location of towns and cities, it looks like you need to generate a collapse in civilization. At least, that might be one tongue-in-cheek take-away from a recent paper by Guy Michaels (London School of Economics) and Ferdinand Rauch (University of Oxford). Michaels and Rauch studied a cool natural experiment - the effect of the fall of the Roman Empire on the location of towns in Britain and France. The key point that makes this natural experiment useful is that the effect of the fall of Rome was much bigger in Britain than in France:
Roman Britain suffered invasions, usurpations, and reprisals against its elite. Around 410CE, when Rome itself was first sacked, Roman Britain's last remaining legions, which had maintained order and security, departed permanently. Consequently, Roman Britain's political, social, and economic order collapsed. From 450-600CE, its towns no longer functioned. The Roman towns in France also suffered when the western Roman Empire fell, but many of them survived and were taken over by the Franks.They find that the location of towns changed in Britain, but remained the same in France. But did that even matter? It turns out it did:
- In short, the urban network in Britain effectively ended with the fall of the western Roman Empire; French towns experienced greater continuity.
- The divergent paths of British and French urban networks allow us to study the spatial consequences of the resetting of an urban network, as towns across Western Europe re-emerged and grew during the Middle Ages.
The conclusion we draw is that many French towns were stuck in the wrong places for many centuries. They could not take advantage of the new transportation technologies since they had poor coastal access; they were in locations that were designed to fit with the demands of Roman times and not the considerations of the Middle Ages.So, towns and cities can be stuck in the 'wrong' (from a productivity perspective) location for centuries or longer. There are no barbarian invasions in our near-term future, so we are to a large extent stuck with the urban locations we have now. This has interesting implications for adaptation to climate change. Many cities currently sit in extremely vulnerable locations, in terms of surface flooding, sea level rise, desertification and water stress, etc. The implications of this paper is that there is substantial inertia that will prevent large-scale relocation of people and industries to areas that are more resilient or less vulnerable. In other words, adaptation to climate change in situ is going to be very important - we can't simply rely on moving away from where the problems occur. On a related note, we shouldn't expect large masses of migrants trying to get away from vulnerable cities and countries to suddenly end up on our doorstep. It simply isn't that easy for them to move.
For the full paper (gated), see here.
[HT: Paul Krugman's NY times blog]