February 2017 Update: Since originally writing this post, there has been a lot of movement internationally to develop a common language for risk. For example, the UN’s “open-ended intergovernmental expert working group on terminology relating to disaster risk reduction” has recently produced a comprehensive glossary of terms. The definitions are easier to read that the long-winded title of the group that created them 🙂
Ebbwater recently completed some research on effective tools for risk assessment. We learnt a lot about the dozens of great tools out there in the big wide world, but we also learned that as Canadians, we do not have a good understanding or common language around risk as it relates to flood. So, here’s our take on some of the common terms that are thrown about when talking to professionals working in the field of flood management.
So starting at the beginning is hazard. Essentially a hazard is something that can potentially cause damage. So for example, water escaping its confines and wetting normally dry areas (i.e., a flood) is a hazard. So is a crack in a sidewalk that might cause someone to trip and fall. In order to ultimately make good decisions on mitigating risk we need to more than the fact that the hazard exists, we need to know where it is, how big a hazard it is (is this a big crack or a little one?), how likely it is to be there, and what is the likelihood or probability it will occur
Now that we’ve established that something bad (a hazard) could happen – it’s time to think about whether it matters or not? Using a twist on the old adage ‘when a tree falls in the forest’ – who cares unless there is something important that will be squished and hurt underneath it? That brings us to vulnerability. Vulnerability describes the susceptibility of a system or community or something else you care about to the damaging effects of the hazard. So in the case of a flood, the vulnerability describes the exposed elements (think of people, their homes and the networks that connect them) on the floodplain (that is normally dry) and how susceptible they are to being damaged by a flood.
If you think about the news stories coming out of disaster areas – what you tend to hear about is the consequences or impacts, because that’s what really matters to people when a hazard strikes. They don’t care about how deep and fast the water is moving – they care that the fast deep water has damaged their home. The consequences or impacts (how badly damaged is the home?) is a function of the hazard (how deep and fast the water is) and the vulnerability (is the home in the way of the deep and fast water?, and was it designed to withstand water?). Consequences and impacts apply equally to more than just damaged homes – for example, was anyone injured or killed? was the local economy slowed? There are a multitude of impact types – but we’ll keep this for another post. For now, have a look at the figure (1) to understand how hazard and vulnerability combine into consequence.
Now, if we loop back to our original definition of hazard – we said that it is partly characterized by the likelihood of it occurring. Broadly (and unscientifically) speaking big hazard events – really big floods or extreme earthquakes happen less often; they are less likely. Smaller events occur more frequently and are therefore more likely and more probable. This is likelihood.
So, looking at Figure 2 we see that Risk is the combination of Consequence and Likelihood, or as the UN-ISDR puts it – it’s the combination of the probability of an event and its negative consequences. Risk is an excellent measure for disaster management – because it allows for the comparison of different scales of events. For example, using this definition of risk – frequent nuisance flooding has similar risk to a single catastrophic flood (Figure 3).
Risk is considered the best measure to think about when planning for natural disasters, as is clearly highlighted in the 2015 Sendai Framework for Disaster Risk Reduction. It’s what Canadian professionals need to be considering for disaster planning. But first, we have to start by better understanding, using and communicating what the term RISK really means.
So our challenge to you is to keep us on our toes. If you hear an Ebbwater staffer use any of the terms above incorrectly – call us out. For every instance we will donate $5 (Canadian of course) to Canadian Red Cross. Feel free to similarly challenge yourself – try making sure you are not using risk when you actually mean hazard or consequence.
For reference here’s some more scientific definitions of terms sourced from international agencies.
Hazard: A potentially damaging physical event, phenomenon, or human activity that may cause the loss of life, injury, property damage, social and economic disruption, or environmental degradation. Hazards can include latent conditions that may represent future threats, and can have different origins: natural (geological, hydrometerorological, and biological) or be induced by human processes. Hazards can be single, sequential, or combined in their origin and effects. Each hazard is characterized by its location, intensity, frequency, and probability. UN-ISDR
Vulnerability: The characteristics and circumstances of a community, system, or asset that make it susceptible to the damaging effects of a hazard. UN-ISDR.
Consequence: The effects on natural and human systems of physical events. (Modified from IPCC)
Likelihood: A probabilistic estimate if the occurrence of a single event or of an outcome. Likelihood may be based on statistical or modelling analyses, elicitation of expert views or other quantitative analyses. (IPCC)
Risk: The combination of the probability of an event and its negative consequences. UN-ISDR