There is a clear line of sight on the broad features of the cities of the future. They will be large, with significantly more than half of the world’s growing population crammed into them.
They will house an increasingly older population, placing stress on services and a rising tax burden on young workers whose taxes pay for those services.
They will be environmentally-constrained, mandating a lower environmental impact of almost every feature of city living we rely on today, and they will need more resilient infrastructure, buildings and economies to accommodate climate change.
In the developing world, the megacities will be a complex and messy mix of formal and informal settlements, with no obvious governance structure covering the entire city.
These are very broad sketches of the challenges. The more interesting issues revolve around how we respond to those challenges, and how those responses affect the design, operation and governance of cities. How we respond will in turn profoundly influence the quality of life of residents and what it feels like to live in such cities.
The future depends on the innovations we create and put in place today. But what form might those innovations take?
Future cities must become smarter, since resources and services will be stretched to their limits. Our cities today are built on projections of long-term needs, and locked into the infrastructure to meet those needs with a large margin of safety, so they are robust against different potential futures.
This is wasteful of materials and energy. Buildings and infrastructure of the future will be fitted with sensors monitoring every aspect of their operation, from climate and energy performance to material safety and service demand.
Energy will flow in real time to where it is most needed. Transport will be directed around areas of high air pollution so human health is preserved. Buildings will be monitored for stresses, allowing actions to be taken before catastrophic failure, reducing the over-engineering of buildings with more concrete and steel than may ever be required.
The same sensors will monitor the climate and allow buildings and infrastructure to respond so that damage from extreme weather events is minimised.
The technologies for climate adaptation are well known. The problem is how to allocate limited technological and financial resources so the overall impact on a city of changing climate is minimised.
This requires understanding of the role of specific parts of the physical city in the economy and services. An approach is needed to rationalise deployment of resources so they are used wisely to protect the city’s economy and services, in turn ensuring livelihoods and well-being are preserved.
Macroeconomic models linked to engineering knowledge allow decision-makers to understand where adaptation and recovery resources can best be directed to get a city back on its feet after an extreme weather event.
Future cities will make increasing use of natural ventilation based on advances in ecology and fluid dynamics.
With the transport system dominated by much quieter electric vehicles, windows will be left open, indoor pollution will be reduced and levels of comfort will rise as the heat island effect disappears.
Improved walking and cycling paths will bring the benefits of exercise and re-connect people to their neighbourhood activities.
Health and well-being will be improved by, rather than be collaterally damaged from, urban life.
At the same time, cities will become living laboratories for sustainability, requiring changes in governance.
Since cities are mixtures of planned and unplanned buildings, formal and informal developments, no single set of solutions to service provision, crime, health or education will work everywhere within a metropolis.
Systems of governance will need to allow for experimentation, testing solutions in some parts of the city but not others, with the design of those trials allowing us to see what works where, and under what conditions.
The messy and complex nature of cities will be turned into an asset, allowing for natural experiments. That in turn will require governance systems that embrace experimentation, politicians who are willing to admit when an experiment has failed and move on to the next experiment, a public that will not penalise those who are brave enough to try something in the face of profound uncertainty and then adjust their decisions when evidence emerges.
Cities will also find an intermediate ground between top-down planning (as in the new towns such as the UK’s Milton Keynes) and bottom-up growth (such as that seen in the favelas of South American cities).
Bottom-up solutions allow for highly local differences in economies, architectural style, materials and energy consumption. However, they can reduce the efficiency of resource use of the city.
The challenge is to design a governance structure that enables the efficiency of technocratic control of planning and development to take place while also allowing citizens to develop solutions that work for their local conditions.
The challenge is to find a system where bottom-up and top-down decisions co-exist comfortably, in other words.
Doug Crawford-Brown is at the Department of Land Economy in Cambridge University; Robert Mair is at the Department of Engineering; and Koen Steemers is at the Department of Architecture. Their original article, which has been shortened slightly, is here