Example - Cities and Hurricanes

Cities and heavily-urbanized areas in the path of hurricanes can demonstrate two different forms of resilience. Hurricanes regularly flood urban areas with water, only for the urban areas to be rebuilt. In theory, urban areas are rebuilt after the disturbance of each hurricane to be better protected against powerful hurricanes, however that may not always be the case. Applying ecological resilience to hurricane management policy, we assume hurricanes to be a persistent, inevitable occurrence and design our cities and hurricane response plans accordingly. Unfortunately, hurricane damage has actually been exacerbated by the policy we have implemented from the mid-20th century to now. This policy is to build higher, stronger levees to keep floodwaters out and storm damage to a minimum.

New Orleans illustrates an overreliance on engineering solutions and the consequences of failing to apply resilience thinking. A hundred years ago, New Orleans was hit by a series of hurricanes, after which it decided to invest in structural upgrades to prevent future flooding (Colten and Giancarlo 2011). The structures’ effectiveness was tested in the 1940s and though it did reduce damage to the city center, the suburbs that had grown beyond the seawall and levees were still heavily impacted by the storm. Post-storm analysis determined that although the suburbs could also be protected from heavy flooding through a more extensive levee system, other factors can play a role in mitigating storm damage. For example, one of the worst affected areas to the east of the city did not have any residential or commercial development and effectively functioned as a buffer. Traditional housing construction methods, which put houses up on raised tiers two or more feet above ground, also contributed to flood prevention (Colten and Giancarlo 2011).

The city nonetheless went all-in on levee construction while simultaneously expanding into low-lying wetlands and other flood-prone areas. With levees in place, housing construction switched to cheaper and more popular methods. City officials, confident that the new levees could withstand anything matching the force of previous hurricanes, largely discounted the threats posed by flooding. They have been repeatedly proven wrong, notably by the flooding done by Hurricanes Betsy, Camille, and Katrina (Figure 7).

Even as hurricanes struck and overcame the levees again and again, the philosophy of rebuilding stronger and better has remained. Instead of changing our tactics, we simply shift the baseline for protection upwards to the strongest hurricane in recent societal memory, only for that baseline to be overcome by future hurricanes.

This philosophy epitomizes engineering resilience, where the metric is how quickly the collapsed system can return, or “bounce back” to its prior state (Angeler and Allen 2016). In this example, a city “bounces back” when it is rebuilt to be the same as it was before the flooding. Although this is an example of “bounce back” resilience, there are downsides to this approach. The city has returned to the vulnerable state it was in pre-flood. Another weather event of sufficient severity would collapse the city once again. On the other hand, ecological resilience requires an understanding of the adaptive cycle as well as a holistic approach: how can policy, science, and engineering use the phases of collapse and reorganization to minimize the consequences of persistent, inevitable hurricanes? Ecological resilience can take other factors into account when protecting our cities from flooding, and can be the key to defending coastal cities from the increasing threats of climate change.

Figure 7: Photographs before and after Hurricane Katrina in Bay St. Louis, Mississippi show the destruction of the coastal structure on the border of the city, as well as massive damage to the city itself. Photo Credits: U.S. National Oceanic and Atmospheric Administration, available under the public domain

 

 

References

Angeler, D.G., and Allen, C.R. 2016. Quantifying resilience. Journal of Applied Ecology, 53: 617-624.

Colten, C.E., and Giancarlo, A. 2011. Losing resilience on the gulf coast: hurricanes and social memory. Environment: Science and Policy for Sustainably Development, 53(4): 6-19.