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  • 1.
    Beven, Keith
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. Lancaster Environment Centre, Lancaster University, Lancaster, UK.
    Almeida, Susana
    Univ Bristol, Dept Civil Engn, Bristol, Avon, England.
    Aspinall, Willy P.
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Bates, Paul D.
    Univ Bristol, Sch Geog Sci, Bristol, Avon, England.
    Blazkova, Sarka
    TG Masaryk Water Resource Inst, Prague, Czech Republic.
    Borgomeo, Edoardo
    Univ Oxford, Environm Change Inst, Oxford, England.
    Freer, Jim
    Univ Bristol, Sch Geog Sci, Bristol, Avon, England.
    Goda, Katsuichiro
    Univ Bristol, Dept Civil Engn, Bristol, Avon, England.
    Hall, Jimw.
    Univ Oxford, Environm Change Inst, Oxford, England.
    Phillips, Jeremy C.
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Simpson, Michael
    Univ Oxford, Environm Change Inst, Oxford, England.
    Smith, Paul J.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster, England;Waternumbers Ltd, Halton Mill, Lancaster LA2 6DN, England.
    Stephenson, David B.
    Univ Exeter, Dept Math & Comp Sci, Exeter, Devon, England.
    Wagener, Thorsten
    Univ Bristol, Dept Civil Engn, Bristol, Avon, England;Univ Bristol, Cabot Inst, Bristol, Avon, England.
    Watson, Matt
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Wilkins, Kate L.
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Epistemic uncertainties and natural hazard risk assessment - Part 1: A review of different natural hazard areas2018Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 18, nr 10, s. 2741-2768Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    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).

  • 2.
    Beven, Keith
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. Univ Lancaster, Lancaster Environm Ctr, Lancaster, England.
    Aspinall, Willy P.
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Bates, Paul D.
    Univ Bristol, Sch Geog Sci, Bristol, Avon, England.
    Borgomeo, Edoardo
    Univ Oxford, Environm Change Inst, Oxford, England.
    Goda, Katsuichiro
    Univ Bristol, Dept Civil Engn, Bristol, Avon, England.
    Hall, Jim W.
    Univ Oxford, Environm Change Inst, Oxford, England.
    Page, Trevor
    Univ Lancaster, Lancaster Environm Ctr, Lancaster, England.
    Phillips, Jeremy C.
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Simpson, Michael
    Univ Oxford, Environm Change Inst, Oxford, England.
    Smith, Paul J.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster, England;European Ctr Medium Range Weather Forecasting, Reading, Berks, England.
    Wagener, Thorsten
    Univ Bristol, Dept Civil Engn, Bristol, Avon, England;Univ Bristol, Cabot Inst, Bristol, Avon, England.
    Watson, Matt
    Univ Bristol, Sch Earth Sci, Bristol, Avon, England.
    Epistemic uncertainties and natural hazard risk assessment - Part 2: What should constitute good practice?2018Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 18, nr 10, s. 2769-2783Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Part 1 of this paper has discussed the uncertainties arising from gaps in knowledge or limited understanding of the processes involved in different natural hazard areas. Such deficits may include uncertainties about frequencies, process representations, parameters, present and future boundary conditions, consequences and impacts, and the meaning of observations in evaluating simulation models. These are the epistemic uncertainties that can be difficult to constrain, especially in terms of event or scenario probabilities, even as elicited probabilities rationalized on the basis of expert judgements. This paper reviews the issues raised by trying to quantify the effects of epistemic uncertainties. Such scientific uncertainties might have significant influence on decisions made, say, for risk management, so it is important to examine the sensitivity of such decisions to different feasible sets of assumptions, to communicate the meaning of associated uncertainty estimates, and to provide an audit trail for the analysis. A conceptual framework for good practice in dealing with epistemic uncertainties is outlined and the implications of applying the principles to natural hazard assessments are discussed. Six stages are recognized, with recommendations at each stage as follows: (1) framing the analysis, preferably with input from potential users; (2) evaluating the available data for epistemic uncertainties, especially when they might lead to inconsistencies; (3) eliciting information on sources of uncertainty from experts; (4) defining a workflow that will give reliable and accurate results; (5) assessing robustness to uncertainty, including the impact on any decisions that are dependent on the analysis; and (6) communicating the findings and meaning of the analysis to potential users, stakeholders, and decision makers. Visualizations are helpful in conveying the nature of the uncertainty outputs, while recognizing that the deeper epistemic uncertainties might not be readily amenable to visualizations.

  • 3. Buchecker, M.
    et al.
    Salvini, G.
    Di Baldassarre, Giuliano
    UNESCO-IHE Institute for Water Education, Delft, the Netherlands.
    Semenzin, E.
    Maidl, E.
    Marcomini, A.
    The role of risk perception in making flood risk management more effective2013Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 13, s. 3013-3030Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Over the last few decades, Europe has suffered from a number of severe flood events and, as a result, there has been a growing interest in probing alternative approaches to managing flood risk via prevention measures. A literature review reveals that, although in the last decades risk evaluation has been recognized as key element of risk management, and risk assessment methodologies (including risk analysis and evaluation) have been improved by including social, economic, cultural, historical and political conditions, the theoretical schemes are not yet applied in practice. One main reason for this shortcoming is that risk perception literature is mainly of universal and theoretical nature and cannot provide the necessary details to implement a comprehensive risk evaluation. This paper therefore aims to explore a procedure that allows the inclusion of stakeholders' perceptions of prevention measures in risk assessment. It proposes to adopt methods of risk communication (both one-way and two-way communication) in risk assessment with the final aim of making flood risk management more effective. The proposed procedure not only focuses on the effect of discursive risk communication on risk perception, and on achieving a shared assessment of the prevention alternatives, but also considers the effects of the communication process on perceived uncertainties, accepted risk levels, and trust in the managing institutions.

    The effectiveness of this combined procedure has been studied and illustrated using the example of the participatory flood prevention assessment process on the Sihl River in Zurich, Switzerland. The main findings of the case study suggest that the proposed procedure performed well, but that it needs some adaptations for it to be applicable in different contexts and to allow a (semi-) quantitative estimation of risk perception to be used as an indicator of adaptive capacity.

  • 4.
    Darmawan, Herlan
    et al.
    GFZ German Res Ctr Geosci, Dept Phys Earth, D-14473 Potsdam, Germany;Univ Gadjah Mada, Fac Math & Nat Sci, Dept Phys, Lab Geophys, Yogyakarta 55281, Indonesia.
    Walter, Thomas R.
    GFZ German Res Ctr Geosci, Dept Phys Earth, D-14473 Potsdam, Germany.
    Troll, Valentin R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik. Univ Padjajaran, Fac Geol Engn, Bandung 45363, Indonesia.
    Budi-Santoso, Agus
    BPPTKG, Jalan Cendana 15, Yogyakarta 55166, Indonesia.
    Structural weakening of the Merapi dome identified by drone photogrammetry after the 2010 eruption2018Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 18, nr 12, s. 3267-3281Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lava domes are subjected to structural weakening that can lead to gravitational collapse and produce pyroclastic flows that may travel up to several kilometers from a volcano's summit. At Merapi volcano, Indonesia, pyroclastic flows are a major hazard, frequently causing high numbers of casualties. After the Volcanic Explosivity Index 4 eruption in 2010, a new lava dome developed on Merapi volcano and was structurally destabilized by six steam-driven explosions between 2012 and 2014. Previous studies revealed that the explosions produced elongated open fissures and a delineated block in the southern dome sector. Here, we investigated the geomorphology, structures, thermal fingerprint, alteration mapping and hazard potential of the Merapi lava dome by using drone-based geomorphologic data and forward-looking thermal infrared images The block on the southern dome of Merapi is delineated by a horseshoe-shaped structure with a maximum depth of 8 m and it is located on the unbuttressed southern steep flank. We identify intense thermal, fumarole and hydrothermal alteration activities along this horseshoe-shaped structure. We conjecture that hydrothermal alteration may weaken the horseshoe-shaped structure, which then may develop into a failure plane that can lead to gravitational collapse. To test this instability hypothesis, we calculated the factor of safety and ran a numerical model of block-and-ash flow using Titan2D. Results of the factor of safety analysis confirm that intense rainfall events may reduce the internal friction and thus gradually destabilize the dome. The titan2D model suggests that a hypothetical gravitational collapse of the delineated unstable dome sector may travel southward for up to 4 km. This study highlights the relevance of gradual structural weakening of lava domes, which can influence the development fumaroles and hydrothermal alteration activities of cooling lava domes for years after initial emplacement.

  • 5.
    Melchiorre, Caterina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Tryggvason, Ari
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Application of a fast and efficient algorithm to assess landslide-prone areas in sensitive clays in Sweden2015Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 15, nr 12, s. 2703-2713Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We refine and test an algorithm for landslide susceptibility assessment in areas with sensitive clays. The algorithm uses soil data and digital elevation models to identify areas which may be prone to landslides and has been applied in Sweden for several years. The algorithm is very computationally efficient and includes an intelligent filtering procedure for identifying and removing small-scale artifacts in the hazard maps produced. Where information on bedrock depth is available, this can be included in the analysis, as can information on several soil-type-based cross-sectional angle thresholds for slip. We evaluate how processing choices such as of filtering parameters, local cross-sectional angle thresholds, and inclusion of bedrock depth information affect model performance. The specific cross-sectional angle thresholds used were derived by analyzing the relationship between landslide scarps and the quick-clay susceptibility index (QCSI). We tested the algorithm in the Göta River valley. Several different verification measures were used to compare results with observed landslides and thereby identify the optimal algorithm parameters. Our results show that even though a relationship between the cross-sectional angle threshold and the QCSI could be established, no significant improvement of the overall modeling performance could be achieved by using these geographically specific, soil-based thresholds. Our results indicate that lowering the cross-sectional angle threshold from 1 : 10 (the general value used in Sweden) to 1 : 13 improves results slightly. We also show that an application of the automatic filtering procedure that removes areas initially classified as prone to landslides not only removes artifacts and makes the maps visually more appealing, but it also improves the model performance.

  • 6. Turkington, Thea
    et al.
    Ettema, Janneke
    van Westen, Cees
    Breinl, Korbinian
    Empirical atmospheric thresholds for debris flows and flash floodsin the southern French Alps2014Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 14, s. 1517-1530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Debris flows and flash floods are often preceded by intense, convective rainfall. The establishment of reliable rainfall thresholds is an important component for quantitative hazard and risk assessment, and for the development of an early warning system. Traditional empirical thresholds based on peak intensity, duration and antecedent rainfall can be difficult to verify due to the localized character of the rainfall and the absence of weather radar or sufficiently dense rain gauge networks in mountainous regions. However, convective rainfall can be strongly linked to regional atmospheric patterns and profiles. There is potential to employ this in empirical threshold analysis. This work develops a methodology to determine robust thresholds for flash floods and debris flows utilizing regional atmospheric conditions derived from ECMWF ERA-Interim reanalysis data, comparing the results with rain-gauge-derived thresholds. The method includes selecting the appropriate atmospheric indicators, categorizing the potential thresholds, determining and testing the thresholds. The method is tested in the Ubaye Valley in the southern French Alps (548 km2), which is known to have localized convection triggered debris flows and flash floods. This paper shows that instability of the atmosphere and specific humidity at 700 hPa are the most important atmospheric indicators for debris flows and flash floods in the study area. Furthermore, this paper demonstrates that atmospheric reanalysis data are an important asset, and could replace rainfall measurements in empirical exceedance thresholds for debris flows and flash floods.

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