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Progression of vulnerability and hazard

Hazards, vulnerabilities and risks - the Pressure And Release (PAR) model.

(Wisner 1994) introduced a model framework to explain how disasters happen, calling it the Pressure And Release (PAR) Model.

PAR model Pressure (Click to expand)

According to the (UNISDR 2017) UN Office for Disaster Risk Reduction – disaster risk is defined as:

The potential loss of life, injury or destroyed or damaged assets which could occur to a system, society or a community in a specific period of time, determined probabilistically as a function of hazard, exposure, and capacity.

(Alexander 2000: 13 cited in Blakie 2004: 50) defined the pseudo-equation used to define risk as:

R = H x V

Risk = Hazard x Vulnerability

But a more sophisticated view is represented in by the qualitative intersection of those exposed to a hazard and the degree of inherent and consequential vulnerability. In order to reduce or otherwise manage risk we can act on any of the three influencing factors:

  • Hazard
  • Vulnerability
  • Exposure

Historically events show us that the effectiveness of hazard management or attempts to reduce the magnitude of the physical agent is limited and, in certain situations, can even be detrimental.

For example, the public often views locations protected by flood assets, such as dams, weirs and sea walls, as safer and, as a result, population densities can increase. While such strategies may reduce the frequency with which smaller-scale events are experienced, large surges will destroy or overrun these barriers, resulting in significant impacts on populations that are unused to flood hazards.

Similarly, there are examples of the relocation of disaster-affected or at-risk communities in order to reduce their exposure, for example (post typhoon Haiyan).

Subsequent evaluations show that relocated populations often suffer from exacerbated vulnerabilities as a result of lost access to services and livelihoods, and move back to or are replaced by new populations in the hazard zone.

We have learned that hazard and exposure management measures are unlikely to be effective and, as a result, we must consider the underlying conditions of the people exposed to such hazards.

PAR model Release (Click to expand)

The PAR model seeks to explain how the intersection of unsafe conditions and hazards creates social vulnerability (Blaikie et al. 1994). PAR is a tool that shows that disasters occur when hazards affect vulnerable people. People’s vulnerability exists as a result of wider social, economic and political conditions or root causes. Vulnerable groups live under pressure where their access to services such as education, healthcare and secure livelihood options are limited, which in turn means limited and unstable income, resulting in poverty, poor health and unsafe living conditions. In order to release these pressures, we must act to reduce the vulnerability component of risk.

Over the last 40 years, we have shifted from a hazard perspective, where we felt we could only respond to the impacts of the hazard, to a more vulnerability-focused view where disaster risk reduction initiatives seek to reduce the underlying causes and effects of vulnerability locally and so limit the potential impacts before they occur. However, the limited capacity of communities and governments means that residual risks are still present and disasters still occur. As a result, communities and agencies must prepare for impact and response.

More recent models, such as Cutter et al. (2008), have promoted an understanding of antecedent conditions and the value of understanding local context.

Tying local knowledge and culture to response interventions can improve strategies for assisting at-risk communities to cope during disasters (ODI 2004: 131).


Alexander, D., (2000). Confronting Catastrophe: New Perspectives on Natural Disasters, New York. Oxford University Press.

Blaikie, P., Cannon, T., Davies, I., Wisner, B. (1994) At Risk: Natural Hazards, People‘s Vulnerability & Disaster. London: Routledge

Cutter, S.L., Barnes, L., Berry, M., Burton, C., Evans, E., Tate, E. and Webb, J., (2008). A place-based model for understanding community resilience to natural disasters. Global environmental change, 18(4), pp.598-606. [online] Available from: Accessed on [8 May 2019]

ODI (2019) As Local as Possible, as International as Necessary: Understanding Capacity and Complementarity in Humanitarian Action [online] Available from [23 Apr 2019]

Twigg, J., (2004). Disaster risk reduction: mitigation and preparedness in development and emergency programming. [online] Overseas Development Institute (ODI). Accessed from: Accessed on: [8 May 2019]

Wisner, B., Blaikie, P., Cannon, T., Davis, I. (2004) At Risk: Natural Hazards, People‘s Vulnerability and Disasters. 2nd edn. London: Routledge (2017). UN Office for Disaster Risk Reduction – Terminology – UNISDR. [online] Available from: Accessed on [8 May 2019]

© Coventry University. CC BY-NC 4.0
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