Revisiting the Foundational “Disaster” Risk Equation

The foundational equation for much of disaster research in the past two decades appeared initially in Blaikie et al. (1994), and was DR= H x V, where disaster risk (DR) is a function not only of a hazard (H) but also of the vulnerability (V) of the impact area. A slightly expanded version by the same author group came out 10 years later (Wisner et al. 2004), but for our purposes here, the original formulation is still wonderfully parsimonious and efficient. We would like to elaborate on the “disaster” concept, however, and expand the equation.

While defining “disaster” has a long history of contention (Quarantelli 1998, Perry and Quarantelli 2005), years earlier Quarantelli (1987) had made another of his fundamental contributions with the argument that the field also needed to more systematically address the “threshold problem” between accidents, emergencies, disasters, and catastrophes, which he saw as conceptually distinct based on their increasingly complex response characteristics and requirements. Subsequently, and inspired by the Hurricane Katrina experience in the southeast United States, Quarantelli (2006) and then Wachtendorf et al. (20 10) argued that “catastrophes” are qualitatively different in response characteristics and long-term effects from “disasters” (see also Holguin-Veras et al. 2014).

Integrating the “threshold” argument, but setting aside accidents as relatively simple events requiring only on-duty personnel from standard response agencies, and adding an exposures (Ex) variable to capture more explicitly what societies have put- and are continuing to put (i.e., risk creation)- in harm’s way, our version of the equation is: EmR/DR/CatR = H + Ex x V, where the risk (R) of an emergency (Em), a disaster (D), or a catastrophe (Cat) is a function of an area’s or community’s hazard (H) plus its human, economic, infrastructure, and environmental asset exposures (Ex)- but crucially, the susceptibilities to harm or vulnerabilities (V) of those asset exposures.

Again setting aside accidents, our shorthand threshold distinctions are that emergencies require the call-up of off duty response personnel, that disasters require external resources and the activation of latent response (e.g., the Red Cross in the U. S. context) and extending organizations (e.g., utility companies and private sector suppliers in the U.S. context), and that catastrophes (diverging somewhat from the current literature) see new or fundamentally changed response organizations and social movements and where, for at least a generation, the collective memory of an event’s impacts are thought of in “Before/After” terms.

There is, of course, a level or unit of analysis problem in this approach. The outcomes of a one­ car automobile accident can be a “catastrophe” for a family. Our solution is to focus analytically on those political-administrative jurisdictions where 80% of the human casualties and/or asset losses occur. Although there will be exceptions with small nation-states, this more disciplined unit of analysis approach avoids defining an event in national terms (e.g., “Chile’s 2010 earthquake and tsunami”) because in most cases event losses are sub-national and geographically concentrated. In the “2010 Chile event,” for example, the losses were overwhelmingly in just two administrative Regiones: Maule and Bio Bio.

From this perspective it is interesting to see where climate change fits into our equation: Because climate change involves hydro-meteorological events (e.g., storms, floods, droughts, heat waves, etc.), it has multiple and varied effects on the initiating or trigger hazard (H) variable, which then has ripple effects across the rest of the equation to yield, ceteris paribus, a much higher risk of emergencies, disasters, and even catastrophes. Understanding climate change in this ripple effect “H” way reinforces the argument that climate change adaptation should be seen as a subset of emergency/disaster/catastrophe risk reduction, because the latter comprises measures to address a range of hazards broader than just hydro-meteorological, including earthquakes, tsunamis, volcanic eruptions, lahars, and others.


Blaikie, Piers, Terry Cannon, Ian Davis, and Ben Wisner, At Risk: Natural hazards, people’s vulnerability, and disasters (London and New York: Routledge, 1994).

Holguin-Veras, Jose, Miguel Jaller, Luk N. Van Wassenhove, Noel Perez, and Tricia Wachtendorf, “Material Convergence: Important and Understudied Phenomenon,” Natural Hazards Review 15/1 (February 2014), pp. 1-12.

Perry, Ronald W. and E. L. Quarantelli (editors), What Is A Disaster? New Answers to Old Questions (Philadelphia: Xlibris, 2005).

Quarantelli, E. L. “Presidential Address: What Should We Study? Questions about the Concept of Disasters,” International Journal of Mass Emergencies and Disasters 5/1 (March 1987), pp. 7-32. This article is the write-up of Quarantelli’ s 1986 Presidential Address to the International Sociological Association.

Quarantelli, E. L. (editor), What Is A Disaster? Perspectives on the Question (New York: Routledge, 1998).

Quarantelli E. L., “Catastrophes are Different from Disasters: Some Implications for Crisis Planning and Managing Drawn from Katrina” (2006),

Wachtendorf, Tricia, Bethany Brown, and Jose Holguin-Veras, “Catastrophe Characteristics and Their Impact on Critical Supply Chains,” Problemitizing Material Convergence and Management Following Hurricane Katrina (Newark, Delaware: Disaster Research Center, 2010).

Wisner, Ben, Piers Blaikie, Terry Cannon, and Ian Davis, At Risk (Second edition): Natural hazards, people’s vulnerability, and disasters (London and New York: Routledge, 2004).