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Vulnerability vs. Resilience

In preparing for my oral exams, I've been thinking about one of the classic questions -- what's the difference between resilience and vulnerability? My answer runs something like this:

First, we need to define the two terms as they're used in the human-environment literature. Both address the question of the impacts of a disturbance on a human or ecological system. Resilience refers to how far a system can be pushed and still bounce back to its old equilibrium. Vulnerability refers to how much impact a given degree of disturbance will have on a system.

1. The two terms are inverses. This is the most common -- and to many, the only -- difference. A vulnerable system lacks resilience, and a resilient system is not very vulnerable. This is true, to some extent. In particular, their moral valence is inverse -- vulnerability is bad, while resilience is good. This is a result of these terms' use mostly in research on environmental and technological hazards, where the interesting changes in the system are the negative ones (forests and houses being flattened by a hurricane, for example). Researchers in the resilience community, however, have pointed out the possible benefits of a lack of resilience -- a process akin to Schumpeterian "creative destruction" that clears out old structures and allows fresh building.

2. The two terms use different types of scales, and imply different visions of the world. Resilience describes a limit -- push the system up to this limit and it will always bounce back, but push it just a bit farther and it will settle into a quite different equilibrium (or disintegrate altogether). This is a categorical type of measurement. Vulnerability, on the other hand, is a continuous measure -- for any amount of disturbance, there is a corresponding degree of change wrought on the system. Thus the idea of resilience is designed for a system that has several discrete equilibrium points (as well as conditions of system destruction) to which the system will gravitate. On the other hand, vulnerability works well for a linear system.

3. Vulnerability is a broader concept. In determining the vulnerability of a system, you must consider both its ability to spring back from disturbance (i.e., its resilience) as well as its resistance to being disturbed. Consider two towns on a hurricane-prone coast. Both towns will collapse (perhaps because the local economy becomes unviable and thus the remaining residents move away) if 50% of the houses are destroyed by a single storm. Yet perhaps for Northtown, a category 3 hurricane would be sufficient to destroy 50% of the houses, whereas Southboro has been blessed with better architects and thus only a category 5 storm will be sufficient to destroy 50% of its houses. Both towns have equal resilience, yet Northtown is clearly more vulnerable, because it has less resistance.

4. Resilience has a built-in time frame, whereas the apparent vulnerability of a system is dependent on the post-disturbance time. Resilience implies the existence of discrete equilibrium points. Thus, to determine a system's resilience, you simply wait for it to arrive at an equilibrium, and then look at whether it's the same as the starting point. With respect to vulnerability, however, it's not clear when the springing-back process can be considered to be finished. In the immediate aftermath of a hurricane, some people may seem to have been extremely vulnerable, as they've lost all their posessions. But if you come back a year later, they may be back where they started (or even better off) because they got a check from the insurance company or rich uncle Phil. On the other hand, in the immediate aftermath the local store may look like it did great, since it was the only undamaged store and thus business is booming. But a year later, enough people may have given up and moved away that the store is facing bankruptcy due to a lack of customers.

None of this is meant to imply that there's a choice to be made between these two concepts, and that one must be a partisan of one side or the other. Each is useful for analyzing different questions, and a clarification such as the above is useful in deciding when each is most applicable.


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