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Abstract: To address many of the problems faced in hydrological engineering planning, design, and management, a detailed knowledge of flood event characteristics, such as flood peak, volume, and duration is required. Flood frequency analysis often focuses on flood peak values and provides a limited assessment of flood events. To develop effective flood management and mitigation policies, estimation of the scale of potential disasters, incorporating the effects of social factors and climate conditions, is required along with quantitative measures of flood frequency. The Japanese flood risk index, the flood disaster occurrence probability (FDOP), was established based on both natural and social factors. It represents the expectation of damage in the case of a single flood occurrence, which is estimated by integrating a physical-based approach as a Total Runoff Integrating Pathways (TRIP) model with Gumbel distribution metrics. The resulting equations are used to predict potential flood damage based on gridded Japanese data for independent variables. This approach is novel in that it targets floods based on units of events instead of a long-term trend. Moreover, the FDOP can express relative potential flood risk while considering flood damage. The significance of the present study is that both the hazard parameters (which contribute directly to flood occurrence) and vulnerability parameters (which reflect conditions of the region where the flood occurred), including residential and social characteristics, were shown quantitatively to affect flood damage. This study examined the probability of flood disaster occurrence using the TRIP model for Japan (J-TRIP), a river routing scheme that provides a digital river network covering Japan. The analysis was based on floods from 1976 to 2004 associated with flood inundation and sediment disasters. Based on these results, we estimated the probability of flood damage officially reported for the whole region of Japan at a grid interval of 0.1 degrees. The relationship between the magnitude of the rain hazard expressed as the probability of exceedance and the probability of flood damage officially reported was expressed as an exponential function by equalizing the whole region of Japan based on excess probability. Moreover, the probabilities of flood damage occurrence according to social factors and changes in climate conditions were also examined. The probability of flood damage occurrence is high, especially in regions of high population density. The results also showed the effect of the dam maintenance ratio on extreme flooding and flood damage frequency. The probability of flood damage occurrence was expected to increase during extreme weather events at the end of this century. These findings provide a sound foundation for use in catchment water resources management. [Copyright &y& Elsevier]

Devastating magnitudes of flood disasters have been occurring in various areas of Japan, and their impact has been increasing in recent years. Looking ahead, it is foreseen that rainfall and its patterns will be altered due to the climate change accompanied by global warming, and there is concern that the intensity and frequency of flood disasters might be exacerbated. This paper aims to introduce flood characteristics and management policies in Japan that have been undertaken for a long time in order to mitigate these recurrent flood disasters. It also highlights extremely devastating floods in some areas that occurred under recent climate variability, and to address the progress in the assessment of hydro-meteorological tendencies and in the promotion of dialogue among climatologists and hydrologists. Lastly, a new initiative to establish an international centre on water-related hazards and its risk management is presented. [ABSTRACT FROM AUTHOR]

Background: The Reiwa First Year East Japan Typhoon of 2019 caused a torrential flood in Japan. In Nagano City, a large area was flooded due to the collapse of the Chikuma River embankment. After large-scale disasters, an increase in cardiovascular and cerebrovascular events has been reported on account of the stressful conditions. However, few reports of disaster-related diseases associated with flood damage have been described. Thus, our aim was to elucidate the effect of floods on the incidences of cardiovascular and cerebrovascular diseases in Nagano City., Methods: The Shinshu Assessment of Flood Disaster Cardiovascular Events (SAVE) trial enrolled 2,426 patients admitted for cardiovascular or cerebrovascular diseases at all five hospitals with an emergency department in Nagano City from October 1 to December 31 in the years 2017, 2018, and 2019. The occurrence of these diseases was calculated in every 2 weeks and the findings of 2019 (year of the flood) were compared with those of 2017 and 2018., Results: Cardiovascular and cerebrovascular diseases significantly increased during the 2 weeks immediately after the flood disaster (149 in 2019 vs average of 116.5 in the previous 2 years, p < 0.05). Unstable angina cases significantly increased 1.5-2 months after the flood disaster, and cerebral hemorrhage cases significantly increased in the 2 weeks after the flood disaster., Conclusions: Cardiovascular and cerebrovascular events increased significantly during the 2 weeks immediately after the large-scale flood disaster caused by the Reiwa First Year East Japan typhoon. Because of the increasing frequency of flood disasters, it is necessary to predict the occurrences of cardiovascular and cerebrovascular diseases and to implement guidelines for their appropriate and timely management., Competing Interests: Declaration of Competing Interests The authors declare that there are no conflicts of interest., (Copyright © 2021. Published by Elsevier Ltd.)

Typhoon Hagibis, which occurred at the beginning of October 2019, was one of the largest and most powerful tropical cyclones and was considered to be the most devastating typhoon to hit Japan in recorded history. Extreme heavy rainfall caused massive impacts to Japan in general and to Marumori Town, Miyagi Prefecture in particular. In the present study, the detailed flood characteristics at Marumori Town were investigated by using field observation and numerical simulations. The obtained data immediately after the flood has clearly shown that most levee breaches were caused by the water overflow on the river embankment at the constriction areas such as the tributaries' junction and the intersection of the river embankment. Numerical simulations were performed to investigate the mechanism of levee breaching in Marumori Town. According to the simulation results, the flooding water from the upstream levee breach locations flowed into the paddy field area and caused the levee to breach at the river embankment interaction in the downstream area. A new levee breach criterion in terms of overflow depth and its duration on the river embankment was proposed. In addition, a sensitivity analysis was also performed to understand the effect of the backwater and phase lag of water level rise between the mainstream and tributaries. Although there have been many studies on flood disasters, the typhoon's flood-induced disasters on the river and coastal infrastructures have still remained a big challenge. The present study outcomes provide useful information not only to understand how the river embankment of tributaries is vulnerable to water level rise, but also to support the river authorities to prepare better mitigation plans for future flood disasters. [ABSTRACT FROM AUTHOR]