Saturday 4 July 2015

Defining "cascading disasters" and "cascading effects"

A common difficulty in researching multi-hazards is that the terminology used in the literature varies greatly, and a standard definition of multi-hazards, cascading hazards etc does not seem to exist. A recent journal article has been published attempting to do just that: define what the term "cascading disasters" and "cascading effects" means.

The paper "A definition of cascading disasters and cascading effects: Going beyond the "toppling dominos" metaphor" by Gianluca Pescaroli and David Alexander first look into the ways in which the terms are used in the present literature. The paper then goes on to dig a little deeper into the drivers that tend to distinguish the phenomena. They conclude with proposing definitions for "cascading effects" and "cascading disasters" to be used going forward when referring to these situations. I include them here as extracts from the full paper, which can be freely obtained here.

"Cascading effects are the dynamics present in disasters, in which the impact of a physical event or the development of an initial technological or human failure generates a sequence of events in human subsystems that result in physical, social or economic disruption. Thus, an initial impact can trigger other phenomena that lead to consequences with significant magnitudes. Cascading effects are complex and multi-dimensional and evolve constantly over time. They are associated more with the magnitude of vulnerability than with that of hazards. Low-level hazards can generate broad chain effects if vulnerabilities are widespread in the system or not addressed properly in sub-systems. For these reasons, it is possible to isolate the elements of the chain and see them as individual (subsystem) disasters in their own right. In particular, cascading effects can interact with the secondary or intangible effects of disasters." - Pescaroli and Alexander, 2015

"Cascading disasters are extreme events, in which cascading effects increase in progression over time and generate unexpected secondary events of strong impact. These tend to be at least as serious as the original event, and to contribute significantly to the overall duration of the disaster’s effects. These subsequent and unanticipated crises can be exacerbated by the failure of physical structures, and the social functions that depend on them, including critical facilities, or by the inadequacy of disaster mitigation strategies, such as evacuation procedures, land use planning and emergency management strategies. Cascading disasters tend to highlight unresolved vulnerabilities in human society. In cascading disasters one or more secondary events can be identified and distinguished from the original source of disaster." - Pescaroli and Alexander, 2015


I very much appreciate and celebrate that this paper has been published (it would have made things a lot easier to have this resource at the beginning of my PhD). There does, however, appear to remain a gap in defining or exploring "cascading hazards", in that the two definitions proposed in the paper include the influence the human or social world has upon disasters or the effects following an initial natural hazard event. This in itself is valuable, yet I would have thought defining "cascading hazards" - the more physical or natural side of the issue - would have been the first place to begin.

Perhaps the authors thought that cascading hazards and the domino or triggering effect had been covered enough in the literature - after all, the title suggests in intention to go beyond the triggering chain of hazards. However, I still think there is a gap in the literature to deal with cascading hazards alone. Indeed, the issues and implications discussed in the paper relating to cascading disasters (such as amplification and interdependencies) are the same or similar issues related to cascading hazards. I guess I will have to wait eagerly for someone to write such a paper (or write one myself).

All-in-all, the paper is likely to prove valuable to the multi-hazard research field. It's value is in the first real attempt to label cascading disasters and cascading effects. Whether the definition becomes more refined or refuted as time goes on, it at least provides a starting point from which to build upon.


Pescaroli, G, and Alexander, D, 2015, A definition of cascading disasters and cascading effects: Going beyond the "toppling dominos" metaphor, Global Risk Forum, GRF Davos Planet@Risk, Volume 3, Number 1, Special Issue on the 5th IDRC Davos 2014, March 2015.