Modeling the Cooperation Network Formation Process for Evacuation Systems Design in Disaster Areas with a Focus on Japanese Megadisasters

Abstract

By treating human relationships as networks, disaster response planners can capture the features of cooperative behaviors between residents, providing valuable insights for effective evacuation planning. In this paper, the writers outline residents' evacuation behaviors during the 2011 Great East Japan earthquake and the resulting nuclear disaster and tsunami. An analysis of these evacuation behaviors shows the significance of cooperation between residents and of problems caused by two types of bias: normalcy and majority syncing. Next, the writers describe how residents' cooperation behaviors accumulate to form cooperation networks and apply the fitness model to the formation of these networks. A case study of network formation in response to a mudslide disaster in the city of Niihama in 2004 is provided. The writers estimate the fitness parameters and analyze the network formation process and structure on the basis of the distribution of the fitness parameters and show the scale-free characteristics of the evacuation phase of this disaster. Disaster response planning can take into consideration the scale-free networks that form around central and bridging players and acknowledge the importance of the role of cooperation behaviors in disasters. E vents related to the Great East Japan earthquake of 2011 required residents to evacuate from areas threatened by the tsunami and by radiation from nu-clear plant meltdowns. Evacuation was complicated not only by damaged and overloaded roads, but also by residents' delays in initiating evacuation behaviors. Generally, people make behavioral decisions during disasters on the basis of information available about the potential danger (e.g., through the mass media, disaster radio and neighbors) and assessment of their ability to evacuate (e.g., ability to travel, dependence on others). The success of mass evacuation frequently relies on co-operation behaviors among residents—for example, information exchange about dangers, safe places and mutual assistance, particularly to aid individuals with low mobility. In Japan, local governments develop and promote local evacuation plans to guide residents' behavior and promote cooperation. Implementing a cooperative evacuation plan is difficult, however, because one can-not know where and when a disaster will occur, and not all residents are sufficiently familiar with the plan before the disaster. To increase the effectiveness of evacuation plans, modeling can be used to provide a practical understanding of the formation of co-operation behaviors. Studies of disaster evacuation have focused on residents' evacuation decision-making behaviors and information acquisition (Katada et al. 2005; Oikawa et al. 2005; Okumura et al. 2001; Yamada and Otazawa 2006). These studies have also examined the relationship between evacuation information dis-semination and the timing of evacuation initiation. In addition, models have been used to develop microsi-mulations of evacuations (Katada et al. 1999). These studies focused on personal evacuation decisions using detailed data on individuals; in this paper, we focus on the cooperation behaviors influencing evacuation. Residents' behavior choices are influenced by the perceived utility of a given action for themselves and for their group, as well as by consideration of others' behaviors; network formation is thus a complex mechanism. Therefore, any approach to analysis should use entire groups of residents (Urata and Hato 2009). In this paper, the writers briefly review events surrounding the 2011 Great East Japan earthquake and describe residents' evacuation experiences during the resulting nuclear and tsunami disasters. The Net-work Formation Model is introduced, considering cooperation behaviors among groups of residents as the networks. The writers then discuss the results of the Network Formation Model and analyze the net-work formation process and network structure using the results of a survey conducted following the 2004 mudslide disasters in the city of Niihama. Finally, im-plications for disaster response planning are discussed.