Skip main navigation

Why are cities complex systems?

The complex structure of cities, and the individual or collective agency of their inhabitants, make interventions complicated
Cartoon of a multi-layered city, stating that cities are complex systems...and they’re made out of people.
© University of Groningen

Christopher Alexander argued that multiple and complex connections and relationships make up a living city.

He explicitly invites you to consider the various possibilities of interaction within the city, for example, your interaction with the traffic system as you stop in front of a red light, which in turn depends on the electricity grid, or the commercial system which enables you to buy something from a corner shop that you have just noticed because you stopped at a traffic light (Alexander 1965).

From these dynamic interactions and overlapping natural, technical, and social systems, slowly emerges the modern picture of the city as a complex system.

Complicated interventions

The complex structure of cities, and the individual or collective agency of their inhabitants, make interventions complicated, as complexity renders (some) outcomes quite unpredictable.

Adaptation action thus requires the careful consideration of complexity. The implementation of adaptation strategies, plans or policies requires continuous monitoring and adjustment to avoid the emergence of unwanted and detrimental consequences.

Such unwanted and/or detrimental consequences may include, for example, an increase in the adaptive capacity of some places, contexts, and people to the detriment of others, or favouring short-term thinking over long-term planning, and vice versa. Moreover, as cities are dependent on other cities and rural areas, these changes are not limited to one urban system but may reverberate through networks (Rozenblat et al. 2018).

On a more positive note, however, this complexity also allows for serendipity; that is, for the unexpected discovery of innovative solutions. For this reason, some authors have advocated planning for something they call ‘urban tinkering’ (Elmqvist et al. 2018). If you are interested in this approach, we recommend the following blogpost to learn more about it.

Global policy frameworks

Let us first adopt a bird’s eye view to see what the situation looks like on a global scale. Contemporary levels of urbanisation have led many authors to conclude that we are now living on an ‘urban planet’ (see, for example, Elmqvist et al. 2018). Only a small percentage of the Earth’s land surface is covered by cities, but urban networks and their (inter-) dependencies span the globe.

What is more, an increasing majority of the world population is leading urban lifestyles. This cultural ‘urbanity’ is often dissociated from the nearby and faraway ecosystems whose services we depend on. An urbanised planet then calls for a global approach to related problems and solutions.

The four key global policy frameworks that are most relevant for urban adaptation are:

  1. The Paris Agreement on Climate Change
  2. The Sendai Framework on Disaster Risk Reduction
  3. The 2030 Agenda for Sustainable Development
  4. The New Urban Agenda


Alexander, Christopher, A city is not a tree (1965): Architectural Form 172.

Elmqvist, Thomas et al, Urban Planet – Knowledge towards Sustainable Cities (2018): Cambridge University Press.

Elmqvist, Thomas et al, Urban tinkering (2018): Sustainability Science 13.

Older, Malka, The Texas Crisis Shows (Again) There’s No Such Thing as a Natural Disaster (2021).

Rozenblat, Celine et al, International and Transnational Perspectives on Urban Systems (2018).

Stockholm Resilience Centre, Tinker, tailor, urban future (2018).

© University of Groningen
This article is from the free online

Sustainable Cities: Governing Urban Adaptation Under Climate Change

Created by
FutureLearn - Learning For Life

Reach your personal and professional goals

Unlock access to hundreds of expert online courses and degrees from top universities and educators to gain accredited qualifications and professional CV-building certificates.

Join over 18 million learners to launch, switch or build upon your career, all at your own pace, across a wide range of topic areas.

Start Learning now