Friday, September 9, 2011

Hazard x (Vulnerability / Resilience) [ x Exposure] = Risk > Impact

Andrew C. Revkin writes an online column for the New York Times (Dot Earth).  On Wednesday he had an insightful column on the wildfires in Texas - - A Hidden Factor Behind Losses in Texas Fires.  His opening paragraph highlights a key issue for engineers and planners:

"The stunning scope of the damage from the wildfires (and set fires) sweeping a Connecticut-size area in Texas is partly a result of extreme drought, but also a function of the extraordinary growth in populations and suburban development in parts of the state in the last half century."

Revkin also writes:

"Given that wildfires are an implicit hazard in Texas, that projections of more intense summer heat from greenhouse-driven are robust and that populations are not likely to shrink any time soon, it would make enormous sense to see fire codes and other standards there reexamined to limit the chances of wildfire jumping into densely populated neighborhoods."

The article alson discussed the classic formula for gauging the scope of the risk from disasters:

Hazard x (Vulnerability / Resilience) [x Exposure] = Risk > Impact

Reukin references the work of David Alexander, who teaches courses in emergency management and humanitarian logistics at the Universita della Svizzera italina in Florence, Italy.  Alexander has a blog (Disaster Planning and Emergency Management) posting that explains in detail the elements of the equation (Theoretical Notes on Vulnerability to Disaster).  Key points in the Alexander posting include the following:
  • Vulnerability is derived from the Latin vulnerare - - meaning "to wound."
  • Vulnerability is difficult to measure.
  • Vulnerability is a latent or inherent property.
  • Vulnerability can be difficult to isolate from risk.
  • Hazard is active and vulnerability is passive.  Risk is not directly caused by vulnerability, but it is greatly, perhaps overwhelmingly, enhanced by it.
  • The inverse of vulnerability is resilience - - where resilience (or capacity, or coping) is the ability to absorb and resist the shock of a disaster.  Engineers will increasingly be tasked to make our systems more resilient - - mainly because things like climate change and extreme weather events are producing an environment in which unpredictability is the new consistency.
  • Vulnerability can be chronic or catastrophic, depending on whether it results in widely diffused malaise or concentrated disaster.  It applies to known risks, adapting risks, emerging risks, and unknown risks.
  • The management of vulnerability must involve holistic techniques that take account of the categories in which it occurs and the different degrees and levels of interaction between them.
  • Low or inaccurate perception of hazard can perpetuate vulnerability, while high perception can lead to its reduction.
  • Given the dynamic environment in which it occurs, measures taken to reduce vulnerability need to be sustainable.
  • Sustainable vulnerability reduction is locally based, supported by the community, well integrated into legislation and planning instruments and part of a grand strategy to make life more resilient for the inhabitants of the area in questions.

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