For my own research [1, 2], I follow the structural risk definition, which simplifies flood risk from a general definition to structural/functional quantities with clear limit state functions.
Eq. 1 (general): risk = probability x consequences
Eq. 2: (structural/functional): risk = failure probability x consequences
Now, in the international literature, the concept of residual risk is also found, e.g. in [3]. This appears in particular in the context of risk communication. In my opinion, both terms describe the same thing. Is that correct? Or do I just not know the difference? I think the term residual risk suggests that the risk can be reduced to zero. So I consider it not very desirable from a technical point of view. At the same time, I also see the difficulty of communicating the risk according to equation 1. What do you think? What experiences have you had?
Many greetings, Niklas
[1]
Article Enriching flood risk analyses with distributions of soil mec...
[2]
Article Geometric and Material Variability of the Probability of Lan...
[3]
Article Managing residual flood risk behind levees: Comparing USA, F...
It is all definitional, with a summary at http://www.ilankelman.org/abstracts/kelman2003frn.pdf and applied for:
(a) UK:
1. https://doi.org/10.1002/j.1477-8696.2001.tb06507.x
2. https://doi.org/10.1007/978-1-4020-4200-3_1
3. http://www.ilankelman.org/articles1/lewisetal.2009corr.pdf
(b) Norway:
5. https://doi.org/10.1111/j.1475-4762.2011.01074.x
6. https://doi.org/10.1111/j.1753-318X.2010.01080.x
In field of flood risk management, risk is often defined as the probability of a flood occurring x consequences.
The residual flood risk is the risk that remains after risk management and mitigation measures have been implemented. It is calculated in exactly the same way as flood risk i.e. probability of the flood occurring x consequences.
The term residual risk actually suggests the risk cannot be reduced to zero.
For example, if a flood defence is constructed that offers a standard of protection of 1 in 100 years (i.e. an annual exceedance probability (AEP) of 1%) it is often assumed, by many people, that the flood risk has been totally eliminated unless a flood which has an AEP rarer than 1% occurs i.e. the flood defence overtops. However, there are a number of ways in which a flood defence can fail before it overtops, hence there is a residual flood risk posed by more frequent floods than the 1% AEP flood.
There is definitely challenge in communicating residual flood risk. This paper may be of interest: Article Managing residual flood risk behind levees: Comparing USA, F...
Thank you Ilan Kelman and Darren Lumbroso for your comments and your commitment to discuss my question. I would like to readjust the focus a little with this addition.
Ultimately, the flood risk (FR) and the " residual risk (RR)" are calculated in the same way. From my perspective, the RR is then only a small value for FR. Further, I now think, why use two words for one and the same thing? In the medium to long term, this only leads to uncertainty and lack of clarity. There are also other technical terms that take up "risk", such as hydrological risk (pure probability calculation without taking into account the consequences in case of an event).
So we should not introduce new terms in an inflationary manner as long as they do not mean added value, and what added value is there in the residual in RR?
I think that it is important that "residual flood risk" and "flood risk" are recognised as separate terms. Although they are both conceptually calculated using the same equation i.e. flood risk = probability of flood occurring x consequences, the processes used for estimating residual flood risk are different from calculating flood risk. Residual flood risk is not necessarily the same thing as "flood risk" and the term residual flood risk does add value because it takes into account all the ways in which flood defences can fail which a simple calculation of "flood risk" may not.
These paper will hopefully explain a bit more as to why residual flood risk is important as a concept:
https://www.icevirtuallibrary.com/doi/abs/10.1680/wama.2008.161.3.169?casa_token=AnMEwZs33LoAAAAA:ydYd_VX32XqLhvgZwOtNdMC9te-AeaGYH0N6jVBp3_spH35TZd51xCio0rfA0bZi9i8mlXPtV6E
https://www.icevirtuallibrary.com/doi/full/10.1680/wame.2002.154.2.109
https://www.sciencedirect.com/science/article/abs/pii/S146290111630003X
Thank you Darren Lumbroso, espescially for providing these additional sources of literature which support a broader view on the wording. After reviewing and rethinking, I would now agree with your explication and state: flood risk and residual flood risk are similar in their calculation but whilst flood risk considers the natural probability of flooding x consequences, the residual flood risk takes into account the failure probability (for any kind of measures) x consequences.
This automatically leads to the economic contribution of flood risk management infrastructure to society.
- Badges
- Science topic
- Similar topics
- Psychology
- Mental Processes
- Learning