Cascading terms in the literature

The term 'cascading' hazards is used inconsistently in the literature, often in passing. It will be used in this blog to describe the phenomenon whereby one hazard triggers another, which triggers another and so on, so that the situation worsens. Cascading hazards are also referred to in the literature as the 'domino/avalanche effect', 'cascading failures', 'catastrophe/disaster chains', 'triggered events' or similar terms (Helbing and Kuhnert, 2003; Delmonaco et al, 2007).

Shi (2005) separates disaster chains into two types: simultaneous and serial chains:

• Simultaneous chains are when multiple hazards occur in a cluster, at the same time and space, causing several disasters concurrently (Shi, 2005).

• Serial chains or synergistic events are a succession of disaster events caused by a single hazard with the resultant disasters happening in turn (Shi, 2005; Marzocchi et al, 2009).

Delmonaco et al (2007) outline two ways of assessing cascading hazards.

The first is by examining an individual chain of events, where one event triggers another, and try to assess the probability values in order to create risk maps (Delmonaco et al, 2007). This approach is input data demanding and ‘the complexity of the hazard chains can be overwhelming’ (Delmonaco et al, 2007).

The second approach is to assess risk for coincidences of hazards, even without assuming a direct link among them (Delmonaco et al, 2007). This is a more ‘robust’ and less data demanding approach that can give a rough estimate of risk posed by cascading hazards (Delmonaco et al, 2007). However, it is questionable whether this ‘overlay’ approach actually conveys a realistic representation of cascading effects.