Resilience and Urban Systems

Resilience and Urban Systems

Given the ambiguity of terms such as "sustainability," some have adopted the idea of "resilience" as a desirable proxy to encourage in human and natural systems. This has some advantages, especially in that resilience, the ability of a system to adapt to changes in internal and external state without degradation, is a measurable characteristic of systems behavior (unlike "sustainability"). But in many ways this is only the beginning of the inquiry.

The most obvious question that arises from any practical consideration of resilience is: resilient to what? For example, a New England salt marsh might be struck by a strong storm, but be resilient because its growth of Spartina (salt hay) is strong enough to dissipate the energy of the waves. But the same marsh might be quite susceptible to catastrophic failure from even a small amount of pollution if it attacks a species in a critical niche, such as Spartina, that has not evolved appropriate defenses. Human systems offer similar examples. For example, the Internet, a “scale free network” characterized by a relatively few well connected hubs and increasingly many less connected ones, is robust in the face of random insult: loss of a few links has virtually no effect on system performance. Such networks, however, are very fragile in the face of planned attack because their architecture relies so heavily on the few well-connected hubs that can be deliberately targeted.

In this age of terrorism and concern about sustainability, urban systems as a whole have become obvious subjects of concern. Security experts worry about the potential vulnerability of such systems to attack, while many environmentalists view them as inherently unsustainable. A resiliency approach, however, suggests a different perspective.

To begin with, urban systems are extremely resilient. Cities have throughout history been destroyed, only to rise again: Hiroshima, Dresden, Moscow, and Budapest are among innumerable cities that have been devastated by war over the past millennium, yet are still vibrant and thriving. Fire or earthquake or both destroyed huge swaths of Tokyo in 1923, Chicago in 1871, and San Francisco in 1906 -- yet they were rebuilt (in the case of Tokyo, historically subject to urban conflagrations for centuries, rebuilt many times). Cities are both extraordinarily resilient, even when completely leveled, and extraordinarily sustainable.

But a closer inspection of urban systems reveals layers of complexity in this resiliency. (Interested readers might want to check out Vale and Campanella's new book, The Resilient City: How Modern Cities Recover from Disaster (Oxford, Oxford University Press, 2005). Most importantly, such resiliency is highly normative in practice. For example, not all components of a stricken city receive the same attention; resources for rebuilding are limited, and the choice of where they are directed is both political and cultural. When Mexico City rebuilt from the devastating 1985 earthquake, for example, representatives of the poor complained that they received nothing, while the wealthy were pandered to. More subtly, the resiliency narratives that shocked populations develop to support their rebuilding can also powerfully express prevailing cultural beliefs and fears. Thus, many contemporary commentators writing after the Chicago fire described looting and pillaging mobs of immigrants and urban poor -- but there is no factual evidence that such events occurred. These narratives both justified direction of recovery resources to the middle class rather than to the poor, and validated an inchoate fear of modernity and change focused on the powerless and the foreign. When Warsaw was rebuilt after its destruction in World War II, care was taken to reconstruct the “Old Town,” thus testifying to Polish rebirth -- but also cementing the legitimacy and ideology of the government imposed on the Poles by the Soviet Union. Resiliency and recovery from disaster are highly normative processes that often say more about the society than those directly involved realize.

Resiliency is thus not only a complicated characteristic of complex adaptive systems (CASs) such as cities, but a highly designed one as well. Moreover, it is that difficult sort of design that is not just explicit, but implicit and often unconscious, for those that might speak of the hidden referents in a recovery process are often silenced by the powerful emotions unleashed by the initial event. Accordingly, those that argue for resiliency even in a good cause such as sustainability should also have to explain what elements of the relevant CAS they want to be resilient, and against what challenges. For resiliency is not an external, objective property, but a human choice reflecting a particular set of values and decisions regarding appropriate allocation of resources, and in a world defined by the human we can not be allowed to escape the implications of our choices.

Brad Allenby is professor of civil and environmental engineering at Arizona State University, a fellow at the University of Virginia's Darden Graduate School of Business, and previously was AT&T's vice president of environment, health, and safety.