Mountain torrents: Quantifying vulnerability and assessing uncertainties

Abstract

Vulnerability assessment for elements at risk is an important component in the framework of risk assessment. The vulnerability of buildings affected by torrent processes can be quantified by vulnerability functions that express a mathematical relationship between the degree of loss of individual elements at risk and the intensity of the impacting process. Based on data from the Austrian Alps, we extended a vulnerability curve for residential buildings affected by fluvial sediment transport processes to other torrent processes and other building types. With respect to this goal to merge different data based on different processes and building types, several statistical tests were conducted. The calculation of vulnerability functions was based on a nonlinear regression approach applying cumulative distribution functions. The results suggest that there is no need to distinguish between different sediment-laden torrent processes when assessing vulnerability of residential buildings towards torrent processes. The final vulnerability functions were further validated with data from the Italian Alps and different vulnerability functions presented in the literature. This comparison showed the wider applicability of the derived vulnerability functions. The uncertainty inherent to regression functions was quantified by the calculation of confidence bands. The derived vulnerability functions may be applied within the framework of risk management for mountain hazards within the European Alps. The method is transferable to other mountain regions if the input data needed are available.

Vulnerability curves vs. vulnerability indicators: application of an indicator-based methodology for debris-flow hazards

“…As far as debris flow is concerned, the first approaches for physical vulnerability assessment were qualitative (Fell and Hartford, 1997;Liu and Lei, 2003;Romang, 2004), including in some cases vulnerability matrices (Leone et al, 1995(Leone et al, , 1996Sterlacchini et al, 2007;Zanchetta et al, 2004) showing a descriptive relationship between the damage and intensity of the flow. However, recently the number of vulnerability curves for debris flows has considerably increased and several studies may be found in the literature Papathoma-Köhle et al, 2012;Quan Luna et al, 2011;Totschnig and Fuchs, 2013;Totschnig et al, 2011). Each vulnerability curve has been developed for a specific area, is based on a particular catastrophic event and expresses the intensity of the process in various ways.…”

“…Efforts to analyse and quantify uncertainties concerning the assessment of physical vulnerability for debris flows have been made in the past (Eidsvig et al, 2014;Totschnig and Fuchs, 2013); however, most of them concern vulnerability curves. Based on the comparison of the two methods and the outline of the advantages and disadvantages of it as far as the assessment of physical vulnerability is concerned a number of recommendations for improvement may be made.…”

Adaptability and transferability of flood loss functions in residential areas

“…Nevertheless, for larger mountain rivers like the Austrian Lech River no study analyzed the general applicability of flood damage models so far as previous investigations aimed mainly on dynamic floods of steep torrent streams (see Totschnig and Fuchs, 2013 for an overview). Hence, it is still an open question to which extent depth-damage functions which are mainly developed for lowland areas can be applied in mountainous regions where floods are characterized by a more dynamical impact.…”

“…Others relied on model intercomparisons (e.g., Bubeck et al, 2011; but did not validate the model performance with real damage data. In the case of mountainous areas, flood loss estimation was only validated for torrent processes (e.g., Totschnig and Fuchs, 2013) but no study addressed larger mountain rivers so far.…”

“…Even if the general consideration of flow velocity in flood damage modeling on buildings cannot be necessarily recommended , the dynamic load of flooding seems to be fundamental for the damage pattern on buildings particularly for mountainous regions like the European Alps (e.g., Totschnig and Fuchs, 2013). In case of torrent processes, such as fluvial sediment transport (e.g., Totschnig et al, 2011) or debris flows (e.g., Fuchs et al, 2007), debris actions, such as the deposition of the accumulated sediment material, influence the relation on building losses remarkably (Totschnig and Fuchs, 2013).…”