Estimating Network Related Risks: a Methodology and an Application in the Transport Sector

Nat. Hazards Earth Syst. Sci., 18, 2273–2293, 2018 https://doi.org/10.5194/nhess-18-2273-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Estimating network related risks: A methodology and an application in the transport sector Jürgen Hackl1, Juan Carlos Lam1, Magnus Heitzler2, Bryan T. Adey1, and Lorenz Hurni2 1Institute of Construction and Infrastructure Management, ETH Zurich, 8092 Zurich, Switzerland 2Institute of Cartography and Geoinformation, ETH Zurich, 8092 Zurich, Switzerland Correspondence: Jürgen Hackl ([email protected]) and Juan Carlos Lam ([email protected]) Received: 19 December 2017 – Discussion started: 2 January 2018 Revised: 16 July 2018 – Accepted: 31 July 2018 – Published: 27 August 2018 Abstract. Networks such as transportation, water, and power 1 Introduction are critical lifelines for society. Managers plan and execute interventions to guarantee the operational state of their net- Managers of networks, such as transportation, water and works under various circumstances, including after the oc- power, have the continuous task to plan and execute inter- currence of (natural) hazard events. Creating an interven- ventions to guarantee the operational state of their networks. tion program demands knowing the probable direct and in- This also applies in the aftermath of (natural) hazard events. direct consequences (i.e., risk) of the various hazard events As the resources available to managers to protect their net- that could occur in order to be able to mitigate their ef- works are limited, it is essential for managers to be aware fects. This paper introduces a methodology to support net- of the probable consequences (i.e., risk) in order to set pri- work managers in the quantification of the risk related to orities and be resource-efficient (Eidsvig et al., 2017). Con- their networks. The methodology is centered on the inte- sequences are often expressed in monetary values, and these gration of the spatial and temporal attributes of the events are distinguished between direct costs (e.g., costs related to that need to be modeled to estimate the risk. Furthermore, clean up, repairs, rehabilitation and reconstruction) and in- the methodology supports the inclusion of the uncertainty direct costs (e.g., in the transport sector, costs related to ad- of these events and the propagation of these uncertainties ditional travel time, vehicle operation and an increase in the throughout the risk modeling. The methodology is imple- number of accidents). Indirect costs have a wide spatial and mented through a modular simulation engine that supports temporal scale (Merz et al., 2010) and are potentially larger the updating and swapping of models according to the needs than direct costs (Vespignani, 2010). of network managers. This work demonstrates the usefulness Conducting a risk assessment can help identify probable of the methodology and simulation engine through an appli- hazard events, and evaluate their impact on networks and cation to estimate the potential impact of floods and mud- users. Nonetheless, conducting such assessments can be a flows on a road network located in Switzerland. The applica- particularly challenging task due to the large number of sce- tion includes the modeling of (i) multiple time-varying haz- narios (i.e., chains of interrelated events) that need to be ard events; (ii) their physical and functional effects on net- taken into account, the modeling of these events, the rela- work objects (i.e., bridges and road sections); (iii) the func- tionships among them, and the availability of support tools tional interrelationships of the affected objects; (iv) the re- to run the models in an integrated way. In building scenarios, sulting probable consequences in terms of expected costs of multiple types of hazards need to be considered, along with restoration, cost of traffic changes, and duration of network the complex nature of networks, specifically their large num- disruption; and (v) the restoration of the network. ber of objects, their spatial distribution, and functional interrelationships. Moreover, it is important to estimate the per- formance of networks during the hazard events and through the recovery to an adequate level of service that is driven by restoration strategies (Lam and Adey, 2016). Therefore, net- Published by Copernicus Publications on behalf of the European Geosciences Union. 2274 J. Hackl et al.: Estimating network related risks work managers need to think of ways to model the cascade rainfall, fault rupture), and ending in the estimation of the of events, interdependencies, and the propagation of uncer- probable consequences of related societal events (e.g., com- tainties (Hackl et al., 2015). munities without access to transportation, water or power ser- As a result of these challenges, risk assessment methods vice). While the methodology is applicable to different types for networks have been the subject of increasing research in- of hazards, networks, regions, sizes of regions, and levels of terest in recent years. Most research has been focused either resolution, the application of the methodology is illustrated on the technical aspects of hazards or those of networks. In on a regional road network in Switzerland prone to floods and the first case, scholars have focused on improving the un- mudflows. Specifically, this work advances the state-of-the- derstanding, the modeling or the prediction of single haz- art in the field of network related risks due to hazard events ard events (Apel et al., 2004; Pritchard et al., 2015; Schlögl as follows. and Laaha, 2016; Pellicani et al., 2017) without explicitly considering the complexity and dynamics of networks. In – The risk of a complete chain of events, from a source the second case, scholars have investigated the vulnerabil- event to its societal events is quantified over space and ity1 (Jenelius et al., 2006; Rupi et al., 2015; Shabou et al., time. In the application, this means considering pre- 2017) or resilience (He and Liu, 2012; Bocchini and Fran- cipitation, runoff, flood, mudflows, (physical) damages, gopol, 2012; Vugrin et al., 2014) of networks due to disrup- functional losses, traffic flow changes, and restoration tions, without evaluating the cause and/or the probability of interventions. The presented links between cascading such disruptions. hydrometeorological hazards, a road network and soci- Some work has been conducted to consider multiple haz- ety will be of interest to the international research com- ards and their effects (i.e., multiple vulnerabilities and con- munity and practitioners working in the fields of net- sequences) in a unified framework (Komendantova et al., work management, urban planning, public policy, and 2014; Mignan et al., 2014; Gallina et al., 2016). Assess- emergency response. ing the risk in such a way is relatively new, and until now only partially developed by experts with different back- – When quantified, risk can be categorized into proba- grounds such as statistics, engineering and various fields of ble direct and indirect costs, with the latter estimated geosciences (Komendantova et al., 2014). Only a limited throughout the hazard events and restoration periods, number of scenario-based and/or site-specific studies have not just immediately after the occurrence of the haz- been proposed due to the difficulty and novelty of the task ard events. In the application, direct and indirect costs (Mignan et al., 2014). Having a diverse team of experts, included costs of interventions, prolongation of travel whose discipline-specific approaches to risk assessment may time, and missed trips, allowing for the evaluation and differ, presents an additional challenge: their contributions comparison of the socio-economic impacts of the mul- are not always easy to aggregate to a level that is useful for tiple hazard scenarios considered. network managers. In addition, current research also shows – The simulation-based approach supports the inclusion the need to take into account the spatial-temporal quantifica- of uncertainties and their propagation throughout the tion of risks across different levels of scale for future sustain- risk model. The application includes results related to able risk management (Fuchs and Keiler, 2008; Fuchs et al., the simulation of 1200 rainfall events, causing floods of 2013). return periods ranging from 2 to 10 000 and, depend- Open research. In conclusion, there has been little work ing on the rainfall intensity and duration, stochastically to bring research outputs concerning the modeling of haz- triggering a number of mudflows in the area. Further- ard events and network vulnerability together in a way that more, as suggested by Lam et al.(2018a), the approach their spatial and temporal uncertain behaviors are assessed in can support the testing of additional scenarios based on a unified framework that fosters multidisciplinary collabora- uncertain relationships (e.g., fragility functions relating tion. hazard intensities with damage state exceedance proba- Contributions. To overcome these challenges, this article bilities). presents the application of a novel risk assessment methodology. The methodology can be used to investigate multiple – A novel simulation engine was constructed as the com- scenarios, starting from the modeling of a source event (e.g., putational platform to estimate risk, supporting the combination of models from different disciplines, and 1Numerous definitions for network vulnerability

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