Epistemic uncertainties and natural hazard risk assessment – Part 1: A review of different natural hazard areas

Abstract

Abstract. This paper discusses how epistemic uncertainties are currently considered in the most widely occurring natural hazard areas, including floods, landslides and debris flows, dam safety, droughts, earthquakes, tsunamis, volcanic ash clouds and pyroclastic flows, and wind storms. Our aim is to provide an overview of the types of epistemic uncertainty in the analysis of these natural hazards and to discuss how they have been treated so far to bring out some commonalities and differences. The breadth of our study makes it difficult to go into great detail on each aspect covered here; hence the focus lies on providing an overview and on citing key literature. We find that in current probabilistic approaches to the problem, uncertainties are all too often treated as if, at some fundamental level, they are aleatory in nature. This can be a tempting choice when knowledge of more complex structures is difficult to determine but not acknowledging the epistemic nature of many sources of uncertainty will compromise any risk analysis. We do not imply that probabilistic uncertainty estimation necessarily ignores the epistemic nature of uncertainties in natural hazards; expert elicitation for example can be set within a probabilistic framework to do just that. However, we suggest that the use of simple aleatory distributional models, common in current practice, will underestimate the potential variability in assessing hazards, consequences, and risks. A commonality across all approaches is that every analysis is necessarily conditional on the assumptions made about the nature of the sources of epistemic uncertainty. It is therefore important to record the assumptions made and to evaluate their impact on the uncertainty estimate. Additional guidelines for good practice based on this review are suggested in the companion paper (Part 2).

Epistemic uncertainties and natural hazard risk assessment – Part 2: What should constitute good practice?

“…Part 2 of this paper constitutes a discussion of some of the issues raised by the review of different natural hazard areas in Part 1 (Beven et al, 2018), with a view to addressing the question of what should constitute good practice in dealing with knowledge related uncertainties in natural hazards assessment. For good epistemic reasons, there can be no definitive answer to the question, only a variety of views.…”

Building hazard maps with differentiated risk perception for flood impact assessment

“…In order to use the methodology in real time, the runtime of the flood forecasting modelling should be below the flow travel time. In this study, a 50-member ensemble forecast was used from Beg et al (2018), where the entire process took 25 min with a three-core desktop in parallel mode to generate a forecast of 12 h. Various per- centile discharges were then run simultaneously in the HD model, which required 30 min to simulate a 12-hour event on an eight-core, 2.4 GHz (Intel E5-2665), including the initial start (Bhola et al 2018a). Post-processing of the model results would consume an additional 15 min.…”

“…In the absence of such infrastructures or with a very large catchment size, HD models can be replaced with alternatives, such as terrain-based models (Zheng et al, 2018) and satellite images (Voigt et al, 2007). In addition, a database of prerecorded inundation scenarios as shown in Bhola et al (2018a) can expand the application of this methodology. Molinari et al (2014) have stated that a comprehensive uncertainty assessment improves emergency responses by assessing the potential consequences of flood events.…”

“…The latter allows faster calculation and has greater stability due to its complex numerical schemes (Martins et al, 2017). Due to these advantages and suitability for use in real-time inundation forecast (Henonin et al, 2013), we have used the diffusive-wave model that was previously set up, calibrated and validated in Bhola et al (2018a) and Bhola et al (2018b). For the diffusive-wave approximation, it is assumed that the inertial terms are less than the gravity, friction and pressure terms.…”

Hazard maps with differentiated exceedance probability for flood impact assessment

“…Although advances are continually being made in real-time forecasting, they are still inherently uncertain (Meyer et al, 2009;Bates et. al., 2014;Beven et al, 2018). The decision-making process based on uncertain predictions can have a huge economic impact and possibly lead to life and death situations (Leedal et al, 2010).…”