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Estimating Spatio-Temporal Risks from Volcanic Eruptions Using an Agent-Based Model

J Jumadi, Nick Malleson, Steve Carver, Duncan Quincey
2020 Journal of Artificial Societies and Social Simulation  
Managing disasters caused by natural events, especially volcanic crises, requires a range of approaches, including risk modelling and analysis. Risk modelling is commonly conducted at the community/regional scale using GIS. However, people and objects move in response to a crisis, so static approaches cannot capture the dynamics of the risk properly, as they do not accommodate objects' movements within time and space. The emergence of Agent-Based Modelling makes it possible to model the risk at
more » ... o model the risk at an individual level as it evolves over space and time. We propose a new approach of Spatio-Temporal Dynamics Model of Risk (STDMR) by integrating multi-criteria evaluation (MCE) within a georeferenced agent-based model, using Mt. Merapi, Indonesia, as a case study. The model makes it possible to simulate the spatio-temporal dynamics of those at risk during a volcanic crisis. Importantly, individual vulnerability is heterogeneous and depends on the characteristics of the individuals concerned. The risk for the individuals is dynamic and changes along with the hazard and their location. The model is able to highlight a small number of high-risk spatio-temporal positions where, due to the behaviour of individuals who are evacuating the volcano and the dynamics of the hazard itself, the overall risk in those times and places is extremely high. These outcomes are extremely relevant for the stakeholders, and the work of coupling an ABM, MCE, and dynamic volcanic hazard is both novel and contextually relevant. impact of certain hazards, and so is important for disaster management. This is traditionally conducted at the community/regional scale using GIS. For example, Biass et al. ( ) successfully analysed risk, focusing on the impact of tephra fallout from the Cotopaxi volcano, and produced several thematic maps that included the social risk level. . Meanwhile, Alcorn et al. ( ) more comprehensively analysed the volcanic risk of Valles Caldera, New Mexico, focusing on testing and demonstrating a GIS-based Multi-Criteria Evaluation (MCE) for risk assessment. Both the hazard and vulnerability were combined based on several criteria using MCE. Similarly, Scaini et al. ( ) used spatial overlay analysis of the hazard and vulnerability maps in GIS to generate risk maps for Tenerife, Spain. Although both Alcorn et al. ( ) and Scaini et al. ( ) present more comprehensive analyses regarding the hazards than Biass et al. ( ), they share a similar limitation with respect to their accounting of the dynamic risks posed to mobile individuals. . Such GIS-based overlay analyses face di iculties in modelling dynamic aspects due to the GIS' inability to handle both space and time appropriately. While static risk analyses can provide spatial risk information that is suitable for assessing the risk to fixed elements, such as buildings, infrastructure, and economic units, they are less appropriate for modelling the risk to those with the ability to move during an emergency in response to unfolding events. Therefore, models that can represent the dynamics of individual risk over time and space are required. Agent-based Models (ABMs), which are able to simulate agent behaviour in non-linear systems (Clarke ; Malleson et al. ; Srbljinović & Škunca ), provide a new approach to risk analysis that focuses on the individuals who are ultimately at risk. However, the concept of individual risk in the typical ABMs of evacuation is less well-developed. Therefore, this paper proposes to use MCE to model individual risks that involve multiple attributes to address this issue. . In an ABM, people are represented as agents who have heterogeneous characteristics and behaviour (Crooks & Castle ) and are able to navigate their environment and interact with other agents. Furthermore, heterogeneity can be introduced into the population of agents, which allows the modelling of individual variations with regards to vulnerability and mobility. The coupling of an ABM with a dynamic hazard model therefore provides an ideal framework through which to represent the dynamic risk to individuals during a volcanic emergency. . ABMs have been used to simulate emergency situations but are limited in terms of taking into account the dynamics of associated risks. The spatial scale of the emergencies as well as the type of hazard vary from buildings (e.g. fire; Shi et al. ( )) to regions (e.g. earthquake, Bernardini et al. ( ); wildfire, Wise ( ); hurricanes, Zhang et al. ( ) and tsunami, Mas et al. ( )). The dynamics of hazard has been commonly implemented; for instance, Mas et al. ( ) used numerical models to simulate inundation due to a tsunami while Wise ( ) used cellular automata to simulate wildfire propagation. However, the dynamic nature of risk includes the interaction of hazards with the elements at risk, especially people, and this was inadequately incorporated into the models used in these examples. . In this paper, we propose a new approach of the Spatio-temporal Dynamics Model of Risk (STDMR) and provide a case study using a pre-developed agent-based evacuation model for Mt. Merapi (Jumadi et al. , ). This approach first creates an individual-level (synthetic) population of agents who live in the area surrounding a volcano. Each agent has a unique vulnerability and, since vulnerability comprises several factors (Cutter et al. ), MCE is used to create a single social vulnerability index for each individual based on his/her place of residence. This is coupled with a dynamic hazard model to capture the dynamics of risk as applied to the individual. The model is able to highlight a small number of high-risk spatio-temporal positions where, due to the behaviour of the individuals evacuating the volcano and the dynamics of the hazard itself, the overall risk at those times and in those places is extremely high. The outcomes are interesting and extremely relevant for the stakeholders, and the work of coupling an ABM, MCE, and dynamic volcanic hazard is both novel and contextually relevant. The paper is organised as follows: in Section , we describe the background concept of the approach; Section then presents the methodology for applying the model and case study; Section provides the results of the experimentation and the spatiotemporal analysis of the results; and, lastly, Section discusses the outcomes and overall conclusion. Background: Modelling the Dynamics of Risk . The previous section discussed the importance of incorporating the spatio-temporal dynamic of a hazard into the modelling of human risk. This section provides the background concept of the approach through the integration of Multi-Criteria Evaluation (MCE) into an ABM. The vulnerability of people to a volcanic hazard is multifaceted, so MCE is a useful technique that can be used to quantify this value (Armas & Gavris ). 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doi:10.18564/jasss.4241 fatcat:hjsukefejjdrjo3civ4lbepg4i