Urban Resilience

Frontier / by Maywa Montenegro /

Merging complex systems science and ecology, resilience scientists have broken new ground on understanding—and preserving—natural ecosystems. Now, as more and more people move into urban hubs, they are bringing this novel science to the city.

In short, cities are the quintessential complex adaptive system. Which makes them, in many ways, the perfect place to explore resilience.
Brian Walker is former program director and chair of the Resilience Alliance, a loose international coalition of natural and social scientists who, in their own words, “collaborate to explore the dynamics of social-ecological systems.” In 2005, recognizing the growing impact of urbanization, the Alliance held a series of brainstorming sessions, laying the groundwork for the “Urban Network,” based out of the Stockholm Resilience Center, an interdisciplinary research group that formed at Stockholm University in 2008.

The Urban Network has research sites in 12 cities: Bangalore, New Dehli, Cape Town, Johannesburg, Chicago, New York City, Phoenix, Canberra, Helsinki, Istanbul, and Stockholm. These cities span the globe and differ vastly in terms of culture, history, and economic development. The ultimate goal, according to Thomas Elmqvist, lead researcher of the Network, is to do a comparative analysis of these cities. How are they similar or different with respect to handling development? How do they compare it comes to withstanding shocks and surprises?

“As humans, we should try to understand how to manage systems in order to avoid passing thresholds,” says Elmqvist. But this is especially difficult in urban contexts, which have already been so transformed by humans that they’ve breached most of the thresholds ecologists are familiar with. When great expanses of concrete and steel now exist where trees and streams once did, new tipping points must be defined for places that are, as Elmqvist puts it, “already tipped.”

Case studies are now underway in each of the Network’s 12 participating cities. But in deciding what kind of data to gather, researchers have had to ask themselves:  What would a city look like through the lens of resilience?


A city’s lifeblood is a continuous flow of stuff—fuel, consumer products, people, and services that enter it either actively, through human effort, or passively through natural processes like solar radiation, atmospheric currents, and precipitation. Ecologists often talk about these resource flows in terms of inputs and outputs. They’ve developed several budgetary models of accounting for them, including the well-known “ecological footprint.”

The resilience approach, according to ecologist Guy Barnett of the Urban Network’s Canberra research team, focuses less on the resources that cities consume and more on the interdependencies along the chain of supply and demand. Dependence on a single type of fuel as an energy source, for instance, creates a highly vulnerable system—especially if fuel prices are volatile or if the supply is prone to disruption.
Consider what happened just outside of Melbourne in 1998. Several explosions at Esso Australia’s natural gas plant there killed two people and halted power supply to the city for nearly two weeks. As a result, the regional dairy industry, which relies on natural gas to power its milk pasteurization, was forced to shut down several of its plants. Some 25 million liters of raw milk went to waste.

So what went wrong? From a resilience perspective, it was partly the drive for efficiency. If the dairies had hedged their risk with backup fuel supplies, building more resilience into the system, milk pasteurization would not have ground to a complete halt. The number of supervisors at the gas plant had been reduced from four to one, and all the engineers had been relocated to the head office in Melbourne, leaving just one person at the controls. Simply having more people could have helped safeguard against catastrophe.

Efficiency per se isn’t the problem, says Barnett. But the way efficiency is conceived, and pursued, is often too narrow. Society strives for efficiency by trying to eliminate apparent redundancies, but things that seemed redundant in a stable climate turn out to be valuable when conditions change. “The quest for increasing efficiency tends to result in systems optimized towards single rather than multiple solutions, centralized rather than distributed organizational responses, all of which are counter to the fundamental concepts of resilience thinking—‘redundancy,’ ‘diversity,’ and ‘modularity,’” says Barnett.

Of course, building in such attributes—contracting with an array of energy suppliers, hiring more engineers—almost always means more money, both in terms of upfront capital investment and long-term management costs. Decisions therefore involve trade-offs between efficiency and resilience, says Barnett, a principle under-acknowledged by many urban planners and policymakers.

Take water, an essential resource for every city—and therefore a chronic source of concern for city managers without an ample supply. An efficient way of getting more would be to tap into groundwater; wealthy cities might even import water from afar. The more resilient approach, according to Elmqvist, would be for city managers to consider the dynamics of the larger watershed. They could negotiate agreements with rural landowners, paying them to manage their property in a way that provides the city with a certain amount and certain quality of water.

“We actually see this happening in a lot of places in Latin America,” says Elmqvist, “Cities are using revenues from water and energy taxes to compensate land owners for landscape management—often by conserving forests to secure a flow of clean water for the city.” A similar scheme is in place in Capetown, South Africa, where the city is paying landowners to remove exotic plants from the watershed. Alien species consume copious amounts of water, so their destruction means more water flows into the streams that eventually reach the city.

Watersheds highlight a simple but crucial point about cities: They are highly dependent, open systems, meaning they consume far greater resources, over a much larger scale, than are available within their own borders. Hong Kong, for instance, depends on a land area 2,200 times its actual size to support its inhabitants—and only 30 percent of this land is Chinese. More than 95 percent of its seafood supply comes from the marine waters of other nations. The resilience of a city, in other words, is highly contingent on the resilience of other places.

The Human Dimension

On the coral reefs around Jamaica, a variety of fish once helped keep algae firmly in check. When intensive harvesting eliminated many of these algae-grazers, long-spined sea urchins took over that niche—and the urchins’ numbers exploded with less competition for food. But then a one-two punch of a bacterial pathogen and a hurricane devastated the urchin population, and algae growth surged, strangling the coral. A coral-dominated system abruptly shifted into a state of algal-dominance.

Abundant biodiversity is critical, as most people know, because it means being able to fill the numerous niches of a healthy ecosystem. But it also increases the odds that some of those species, like fish and urchins, will share niches and have overlapping roles in the ecosystem. This redundancy can help a system absorb disturbance—or when it’s lost, make it vulnerable to attack. In the case of the Jamaican reefs, an infection or storm that might once have been easily surmountable suddenly become lethal.

When it comes to human populations, ecologists are hesitant to stretch metaphors too far—a biodiverse ecosystem is not the same as a diverse population. (After all, says Elmqvist, a very heterogeneous society can also mean a lot of conflict). On the other hand, he says, a good analogy can be drawn to ecosystem redundancy.

“It’s important that you have institutions and functions in society that also overlap,” says Elmqvist. “If one member of the group is lost, there will be another that can maintain the function, so the function of the system as a whole is maintained.”

Tags cities ecology research resilience systems

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