Melanie S. Kappes

Challenges of analyzing multi-hazard risk: a review

Many areas of the world are prone to several natural hazards, and effective risk reduction is only possible if all relevant threats are considered and analyzed. However, in contrast to single-hazard analyses, the examination of multiple hazards poses a range of additional challenges due to the differing characteristics of processes. This refers to the assessment of the hazard level, as well as to the vulnerability toward distinct processes, and to the arising risk level. As comparability of the single-hazard results is strongly needed, an equivalent approach has to be chosen that allows to estimate the overall hazard and consequent risk level as well as to rank threats. In addition, the visualization of a range of natural hazards or risks is a challenging task since the high quantity of information has to be depicted in a way that allows for easy and clear interpretation. The aim of this contribution is to give an outline of the challenges each step of a multi-hazard (risk) analysis poses and to present current studies and approaches that face these difficulties.

Medium-Scale Multi-hazard Risk Assessment of Gravitational Processes

This section discusses the analysis of multi-hazards in a mountainous environment at a medium scale (1:25,000) using Geographic Information Systems. Although the term ‘multi-hazards’ has been used extensively in literature there are still very limited approaches to analyze the effects of more than one hazard in the same area, especially related to their interaction. The section starts with an overview of the problem of multi-hazard risk assessment, and indicates the various types of multi-hazard interactions, such as coupled events, concatenated events, and events changing the predisposing factors for other ones. An illustration is given of multi-hazards in a mountainous environment, and their interrelationships, showing triggering factors (earthquakes, meteorological extremes), contributing factors, and various multi-hazard relationships. The second part of the section gives an example of a medium scale multi-hazard risk assessment for the Barcelonnette Basin (French Alps), taking into account the hazards for landslides, debris flows, rockfalls, snow avalanches and floods. Input data requirements are discussed, as well as the limitations in relation to the use of this data for initiation modeling at a catchment scale. Simple run-out modeling is used based on the energy-line approach. Problems related to the estimation of temporal and spatial probability are presented and discussed, and methods are shown for estimating the exposure, vulnerability and risk, using risk curves that expressed the range of expected losses for different return periods. The last part presents a software tool (Multi-Risk) developed for the analysis of multi-hazard risk at a medium scale.

ASCHFLOW : a dynamic landslide run-out model for medium scale hazard analysis

BackgroundLandslides hazard analyses entail a scale-dependent approach in order to mitigate accordingly the damages and other negative consequences at the respective scales of occurrence. Medium or large scale landslide run-out modelling for many possible landslide initiation areas has been a very difficult task in the past. This arises from the inability of the run-out models to compute the displacement with a large amount of individual initiation areas as it turns out to be computationally strenuous. Most of the existing physically based run-out models have difficulties in handling such situations. For this reason, empirical methods have been used as a practical mean to predict landslides mobility at a medium scale (1: 10,000 to 1: 50,000). They are the most widely used techniques to estimate the maximum run-out distance and affected zones not only locally but also regionally. In this context, a medium scale numerical model for flow-like mass movements in urban and mountainous areas was developed.Results“AschFlow” is 2-D one-phase continuum model that simulates, the entrainment, spreading and deposition process of a landslide or debris flow at a medium scale. The flow is thus treated as a single phase material, whose behavior is controlled by rheology (e.g., Voellmy or Bingham). The model has been developed and implemented in a dynamic GIS environment. The deterministic nature of the approach makes it possible to calculate the velocity, height and increase in mass by erosion, resulting in the estimation of various forms of impacts exerted by debris flows at the medium scale.ConclusionsThe developed regional model “AschFlow” was applied and evaluated in well documented areas with known past debris flow events. The “AschFlow” model outputs can be considered as an indication of areas possibly affected with a defined intensity for one or more landslide events. From a user perspective the “AschFlow” model can be seen as a standalone model which can be utilized for a first assessment of potentially impact areas.

Methods for Debris Flow Hazard and Risk Assessment

Debris flow events yield a threat to different components of mountainous environments not only as the result of the process evolution but of the interaction with human systems and their coupled vulnerabilities. A variety of models exists for characterising the hazard that the different mass-flow phenomena present. In the case of dynamic run-out models, they are able to forecast the propagation of material after the initial failure and to delineate the zone where the elements at risk will suffer an impact with a certain level of intensity. The results of these models are an appropriate input for vulnerability and risk assessments. An important feature of using run-out models is the possibility to perform forward analyses and forecast changes in hazards. However, still most of the work using these models is based on the calibration of parameters doing a back calculation of past events. Given the number of unknown parameters and the fact that most of the rheological parameters cannot be measured in the laboratory or in the field, it is very difficult to parameterize the run-out models. For this reason the application of run-out models is mostly used for back analysis of past events and very few studies attempts to achieve a forward modelling with the available run-out models. A reason for this is the substantial degree of uncertainty that still characterizes the definition of the run-out model parameters. Since a variety of models exists for simulating mass-flows and for identifying the intensity of the hazardous phenomena, it is important to assess these models, perform a parameterization and reduce their uncertainties. This will enable to improve the understanding to assess the hazard and will provide the link with vulnerability curves that will lead eventually to generate risk curves and quantify the risk.

Landslides in a Multi-Hazard Context

Landslides and other hazards are components of natural systems and thus are often related to each other. Since these relationships may result in unexpected effects, an approach to account for these relationships in a regional multi-hazard study is proposed. Subdivided into relations concerning disposition alteration and hazard chains in which one process triggers another process, the hazard links are identified and studied by means of GIS-based methods. Two techniques are used for the implementation of relations into the analysis procedure, the establishment of feedback loops and the overlay of hazard areas to determine overlaps. Such a regional analysis enables in the first place the definition of those areas possibly affected by unexpected effects due to hazard relations and indicates the spots to be studied in detail by local and detailed methods to quantify the potential consequences.

Index-Oriented Methodologies for Landslide Consequence Analysis: An Application to a Mountain Community in the French Alps

Consequence analysis is a key aspect of anchoring assessment of landslide impacts to present and long-term development planning. Although several approaches have been developed over the last decade, some of them are difficult to apply in practice, mainly because of the lack of valuable data on historical damages or on damage functions. In this paper, two possible consequence indicators based on a combination of descriptors of the exposure of the elements at risk are proposed in order to map the potential impacts of landslides and highlight the most vulnerable areas. The first index maps the physical vulnerability due to landslide; the second index maps both direct damage (physical, structural, functional) and indirect damage (socio-economic impacts) of landslide hazards. The indexes have been computed for the 200 km2 area of the Barcelonnette Basin (South French Alps), and their potential applications are discussed.

The Use of Geo-information and Modern Visualization Tools for Risk Communication

Clear communication of information is a compulsory issue in disaster risk management. This section highlights the development of interactive tools to constantly present the most recent geo-database with multi-scale and multi-source approaches, and user-oriented graphical interfaces for simple and quick data management. A client-server structure is used to customize geo-data accessibility rights and interaction and a WebGIS service architecture is designed to offer data accessibility and effective dissemination to the user community. Different solutions are presented using a common open source environment and interoperability plug-ins: (1) WebRiskCity is an educational kit on multi-hazard risk assessment, (2) Barcelonn@ supports risk management with interoperability on spatial data and metadata, (3) Historic@ is a prototype to spatially compare historical natural events and population trends, and (4) MultiRISK Visualisation Tool is a service to automatically publish multi-hazard risk analysis outcomes produced by the MultiRISK Modelling Tool.