Numerical simulation and modeling became an essential technology in tsunami research and disaster management. Various numerical models were proposed and utilized for the development of tsunami risk assessment, inundation maps, and evacuation plans. The model verification and validation standards would be crucial to ensure sufficient reliability of tsunami risk assessment, inundation maps, as well as a consistency among various efforts. Common approach to ensure sufficient accuracy and reliability of numerical modeling is developing benchmark problems of hydraulic experiments and to use them for numerical model’s verification and validation.

To satisfy this requirement, “Tsunami Modeling Hackathon” was held in September 2020 to organize new benchmark problems in numerical modeling of tsunamis and to improve their reliability and accuracy. Hackathon is an intensive-gathering event of computer programmers and others involved in software development to create outcomes by the end of the event. This event was organized by Prof. Tomoyuki Takahashi of Kansai University and his colleagues, who led the tsunami research subcommittee in Japan Society of Civil Engineers (JSCE).

Tsunami modeling hackathon, in which about 23 teams and 162 researchers joined, included experiment and modeling teams in seven benchmark problems: urban tsunami inundation, landslide tsunami, tsunami loading on seawalls and coastal structures, sediment transport, drift of floating objects. The modeling groups performed the blind tests to cross-validate and interpret the results of their simulations in seven benchmark problems given by the experiment groups and discussed the improvement.

This special issue reports the outcomes of the tsunami modeling hackathon, and includes six papers (five in this issue, one in the regular issue). We hope this issue will provide useful insights for tsunami modelers and contribute to establishing a standardized way to ensure that various tsunami numerical models would be validated through the benchmark problems.

The detailed understanding of tsunami hazard risk using numerical simulations requires a numerical model that can accurately predict tsunami inundation phenomena on land. In such models, the structural effects are indirectly considered using the variation of bottom roughness as a proxy for the differences in building densities. Only a few studies have conducted intermodel tests to investigate tsunami inundation in complex coastal urban cities. During the tsunami analysis hackathon held in September 2020, eight research groups met to have a detailed discussion on the current urban inundation problems. In this study, we conducted an intermodel comparison of the numerical tsunami models, using the data from physical experiments that were performed on a detailed urban model. Our objective was to investigate the necessary conditions of an accurate numerical model based that can ensure high reproducibility and practicality. It was confirmed that the accuracy of topographic data is an important parameter for tsunami inundation simulations in complex urban areas. Based on the computational cost and accuracy, we suggest that a resolution of 1 cm of topographic data is a sufficient condition for tsunami inundation simulations on 1/250 scale model.

Tsunami generation due to a landslide has been simulated using various numerical models, and the resulting water surface displacements from the models, as well as the corresponding experimental data, are compared. The numerical models used in this study are a two-layer long-wave model, a two-level non-hydrostatic model, a three-dimensional model, a lattice-Boltzmann-type model, an SPH-type model, and an MPS-type model. Tsunamis generated by a fluid falling down a uniform slope are accurately reproduced by the models, especially when the wave height of the tsunami is not large. When using the two-layer long-wave model, in which the two layers of a falling fluid and seawater are assumed not to mix, the parameters including the seabed friction coefficient, adjusted in one case, are not appropriate for other mixing conditions. The two-level model with non-hydrostatic pressure exhibits wave disintegration owing to the effects of both nonlinearity and dispersion, although the second wave generated by the reflection of a wave traveling towards the shore is not simulated accurately. Tsunamis caused by a group of rigid cylinders falling down a uniform slope have also been simulated using two Lagrangian models, namely the SPH- and MPS-type models. Although the first peak at the water level is accurately reproduced by both models, the water level at the trough between the first and second crests is overestimated.

The prediction performance of numerical models of tsunami wave pressure on land structures was investigated using blind tests. Two types of numerical models were used, based on the volume-of-fluid (VOF) method. Both models reproduced the experimental results well for water-level time series. For wave-pressure time series, some differences were observed between the two models in the vertical distribution of wave pressure during the initial rise. In both models, however, the experimental results showed that overall trends for total wave force were in good agreement. The experimental results produced a value slightly higher than the maximum wave force, suggesting that caution is needed when designing structures to ensure that wave force is not underestimated.

Tsunami sediments provide direct evidence of tsunami arrival histories for tsunami risk assessments. Therefore, it is important to understand the formation process of tsunami sediment for tsunami risk assessment. Numerical simulations can be used to better understand the formation process. However, as the formation of tsunami sediments is affected by various conditions, such as the tsunami hydraulic conditions, topographic conditions, and sediment conditions, many problems remain in such simulations when attempting to accurately reproduce the tsunami sediment formation process. To solve these problems, various numerical models and methods have been proposed, but there have been few comparative studies among such models. In this study, inter-model comparisons of tsunami sediment transport models were performed to improve the reproducibility of tsunami sediment features in models. To verify the reproducibility of the simulations, the simulation results were compared with the results of sediment transport hydraulic experiments using a tsunami run-up to land. Two types of experiments were conducted: a sloping plane with and without coverage by silica sand (fixed and movable beds, respectively). The simulation results confirm that there are conditions and parameters affecting not only the amount of sediment transport, but also the distribution. In particular, the treatment of the sediment coverage ratio in a calculation grid, roughness coefficient, and bedload transport rate formula on the fixed bed within the sediment transport model are considered important.

Assessing the risk of tsunami-driven debris has increasingly been recognized as an important design consideration. The recent ASCE/SEI7-16 standard Chapter 6 requires all the areas included within a 22.5° spreading angle from the debris source to consider the debris impact. However, it would be more reasonable to estimate the risks using numerical simulation models. Although a number of simulation models to predict tsunami debris transport have been proposed individually, comparative studies for these simulation models have rarely been conducted. Thus, in the present study, an inter-model comparison for tsunami debris simulation model was performed as a part of the virtual Tsunami Hackathon held in Japan from September 1 to 3 in 2020. The blind benchmarking experiment, which recorded the transport of three container models under a tsunami-like bore, was conducted to generate a unique dataset. Then, four different numerical models were applied to reproduce the experiments. Simulated results demonstrated considerable differences among the simulation models. Essentially, the importance of accurate modelling of a flow field, especially a tsunami front, was confirmed to be important in simulating debris motion. Parametric studies performed in each model and comparisons between different models also confirmed that a drag coefficient and inertia coefficient would influence the simulated debris trajectory and velocity. It was also shown that two-way coupled modelling to express the interaction between debris and a tsunami is important to accurately model the debris motion.

We are very pleased to publish this Mini Special Issue, dedicated to NIED Frontier Research on Science and Technology for Disaster Risk Reduction and Resilience 2021. Three papers and one survey report are included.

Miura et al. indicate the scope of disaster prevention covered by the new courses of study in the field of disaster prevention. By visualizing the contents of classification and analysis, they propose how to handle the scope of disaster prevention in disaster prevention learning in consideration of the comprehensiveness to solve the problems. In the second paper, a case study on flood damage in Hitoyoshi, Kumamoto Prefecture, Mizui and Fujiwara analyze a method of immediately determining the amount of waste disposal work and the number of residents and disaster volunteers required in the event of a disaster. Fujiwara et al. study the feasibility of estimating damage to large-spanned building structures by conducting shake table tests on a small gymnasium model with simulated damage and measuring the natural frequencies and mode shapes. Onoue et al., in a work published as a survey report, present a method for analyzing slope displacement by using the distance image data of a depth camera. They indicate the possibility of detecting minute changes that can precede slope failure.

We hope this issue provides information useful to all readers who study natural disasters.

In the New Courses of Study revised in March 2017, the contents of safety education, including disaster prevention, were significantly enhanced compared with the previous Courses of Study (2008). This can be attributed to the 2011 Great East Japan Earthquake and an increase in the frequency of subsequent natural disasters, as well as changes in the education curriculum stipulated by the Courses of Study, such as the introduction of active learning. Associated with this change, in the field of education, contents that conform to the curriculum of each subject are required. In this research, we first focus on how the contents of the Courses of Study related to disaster prevention have changed in recent years, and discuss what drove the change. In addition, we classify and analyze, in terms of elementary schools, the system of the educational contents related to disaster prevention included in the New Courses of Study. By visualizing the contents of our classification and analysis, we indicate the scope of disaster prevention covered by the New Courses of Study in the field of disaster prevention. Subsequently, we propose ways to manage the scope of disaster prevention in disaster prevention learning in consideration of the comprehensiveness to address the problem.

In recent years, a wide-area disaster causing enormous damage has occurred almost every year in Japan. The authors have been involved in the management of disaster volunteer centers in various places and have realized the difficulty in coordinating the actual number of activities in disaster-stricken areas and the required number of disaster volunteers. The number of disaster volunteers required varies greatly on a daily basis. The number of volunteer activities often depends on the quantity of disaster waste created from damaged houses. Accordingly, if the quantity of waste was grasped immediately on the spot, the number of disaster volunteers required in the short term could be estimated. In this study, the actual conditions in Hitoyoshi City, Kumamoto Prefecture, at the time of the Heavy Rainfall in July 2020 are considered as an example, and the method is considered to immediately grasp the quantity of waste to be disposed of and the number of people required for this task. We compared the amount of waste disposal work estimated from the in-vehicle camera image with the number of active residents and volunteers. As a result, it was estimated that 40–50% of the work was carried out by volunteers at the peak of volunteer activities.

In this study, the authors used shake-table tests to assess the modal parameters of a small-scale gymnasium model with simulated damage, the feasibility of estimating the damage to large-span building structures was studied. In Japan, large-span structures, such as gymnasiums, are expected to be used as evacuation shelters when a natural disaster occurs. As the shelter itself may be damaged in case of an earthquake, it is critical to determine whether damage has occurred, where it occurred, and how serious it is, before the shelter is used. The small-scale gymnasium was designed based on the similarity rule. Observed earthquake ground motions scaled to aftershock levels were applied to the model. The natural frequencies and mode shapes were obtained from the measured response accelerations. To study the influence of structural damage on the modal parameters, a gymnasium model with simulated damage was also tested. The results indicate that the modal parameters, e.g., natural frequencies and mode shapes, can be obtained from the response accelerations, and the damage patterns can be estimated from the changes in these modal parameters.

Sediment disasters have occurred with higher frequencies in recent years because of local heavy rains caused by line-shaped precipitation systems and torrential rains accompanying large typhoons. Since rescue operators are constantly under physical risk at disaster sites, there is a need for technologies to predict the occurrence of secondary disasters. The authors research the measurement of slope displacements by focusing on a depth camera that is readily deployable, can be easily set up, and enables monitoring of an extensive area but does not require expert knowledge to carry out measurements. In this process, we confirmed the difficulty of measuring slope changes preceding failure when the depth camera (DC) is set at a distance because of the large measurement errors caused by the limited depth resolution and poor measurement conditions under rainfall. In this study, we propose a new method for analyzing depth image data obtained by a depth camera and verify its validity for displacement measurements. After comparing the previous and proposed methods, we could confirm that the latter enables one to detect slope changes from minute deformations. When compared with the results of extensometers that directly measured the slope, we found that the results displayed similar tendencies of increase. Therefore, by measuring displacements preceding a slope failure using a depth camera and analyzing the depth image data acquired using the proposed method, we found that it is possible to detect minute changes that precede slope failures.

The lack of adequate knowledge sharing and knowledge creation about disasters and climate change has been identified as a reason behind the unsatisfactory performance of climate-adaptation and disaster-management practices. This study aimed to identify the critical factors in knowledge creation in order to improve community resilience and propose a conceptual model. The main objectives of this study were to i) identify the key factors supporting the creation of knowledge, ii) identify the key factors promoting community resilience, and iii) develop a conceptual model to improve community resilience based on knowledge creation. This study used both quantitative and qualitative methods. A cross-sectional analysis was conducted in four coastal subdistricts in Banda Aceh, Indonesia. A total of 300 samples were obtained from among respondents living in the coastal area using a purposive random sampling technique. The paper presents a literature review exploring theories and concepts concerning the factors supporting knowledge creation as a way to increase community resilience. A conceptual framework is then generated based on the results of field surveys and prior studies. The knowledge-level survey results indicate a need to develop a community resilience framework based on Knowledge Creation Theory as the foundation for decision making and ensure the transmission of knowledge across generations. This study proposes a conceptual model of Knowledge Creation for Community Resilience (KCCR).

Clarification of the individual factors determining the speed and quality of life recovery after massive disasters is crucial in assessing the vulnerability and resilience of individuals and communities. The research, however, remains in its infancy in that the index of life recovery per se is yet to be established; researchers have utilized different sets of variables, and their importance seems to vary across recovery phases potentially reflecting the change in housing situation. In addition, previous research on promoting factors of life recovery has primarily focused on demographic factors and inadequately addressed the psychological and behavioral factors, which has large educational and cultural implications. In this study, to address these two issues, we analyzed the survey data of the 2011 Great East Japan Earthquake and Tsunami disaster. First, from the multiple questionnaire items relevant to the situations of life recovery, we extracted the major elements by factor analysis and investigated their relationship to subjective sense of life recovery. At this time, we compared the relationships obtained between victims who lost their housing and those who did not. Then, we examined the psycho-behavioral as well as demographic factors promoting these life-recovery elements. The factor analysis provides two recovery elements: Well-being (health and social connections) and Housing Recovery (integrity of residential environment). The main determinant of subjective sense of life recovery was the housing recovery element for victims who had lost their houses, while it was the well-being element for those who did not experience housing loss. Among the demographic factors, a robust effect of income on the housing recovery element was identified in both victim groups while the effect of age and household structures on the two elements varied between groups. We clarified that different psycho-behavioral factors promoted two life-recovery elements. Across groups, contribution of leadership to the housing recovery element and that of neuroticism (negative), emotional regulation, and active well-being to the well-being element were identified. The former finding is consistent with the importance of consensus building in housing reconstruction, and the latter may reflect the role of common psycho-behavioral capacity oriented to individuals’ well-being including social aspects. The two life-recovery elements and their promoting factors thus identified may provide a parsimonious macroscopic framework for the evaluation and promotion of life recovery from disasters, and have practical utility for an educational approach to strengthening community resilience.

In this study, an education program for heavy rainfall risk management was developed using the Analysis, Design, Development, Implementation, and Evaluation (ADDIE) model of instructional design (ID) to enhance the disaster response capabilities of schoolchildren to encourage them to think and act responsibly to protect themselves during a disaster following heavy rainfall. The program’s effectiveness was evaluated by its implementation at Nagaoka Municipal Senju Elementary School in Nagaoka City, Niigata Prefecture, which was devastated by the heavy rainfall caused by 2019 Typhoon No.19. The learning effect was confirmed throughout the program. Furthermore, the program has improved because of its implementation and evaluation.

During the early stages of the COVID-19 pandemic in 2020, state governments all over the world were forced to respond to the crisis, prioritizing not only inbound activities but also their citizens abroad. Our study focused on the reasons for the differences in the evacuation operations, procedures, and outcomes in each country. This study focused on Asian countries/territories that experienced the pandemic earlier than other regions, to compare their prompt evacuation processes between January and May, 2020. Data on the evacuation missions and COVID-19 situation in each studied country/territory were collected. The evacuation operations were reviewed and analyzed using the Business Process Model and Notation to identify the differences that made some of the operations more effective. The insight can contribute to future adaptation and development to implement more effective operations during the emergency response to a pandemic.