This is a field survey report on the heavy rainfall disaster that occurred in the Higashimikawa area of Aichi Prefecture on June 2, 2023. The total amount of precipitation at AMeDAS Toyohashi was 418 mm in 24 hours, the largest rainfall in the statistical history. Two rivers overflowed around 4:30 p.m., causing flood damage in the surrounding areas. In the Yagyu River, water flowed into an area where the ground level was lower than the surrounding area, resulting in a maximum inundation depth of 84 cm. In the Umeda River, the maximum inundation depth was 63 cm where the point near the overflow point. The results of the investigation showed the levee was not damaged, suggesting that the levee had a significant effect in mitigating the damage.

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On July 3, 2021, a debris flow caused a total of 27 deaths and missing persons in the Aizome River in Atami City, Shizuoka Prefecture. This damage was the largest number of victims from a sediment disaster in one location since 1982. When compared to five sediment disasters that caused similar levels of victims, the slope gradient of the Aizome River was similar to the other cases. The amount of sediment spilled was also not particularly large compared to other cases. The Aizome River has a longer steep channel section than other cases, and houses were densely built along it. This feature may have been a contributing factor to the large number of victims. On the other hand, the number of victims relative to the number of lost or collapsed houses in the Aizome River was low. This could be due to the following reasons: 1) calls for evacuation had already begun, 2) it was daytime and people were more likely to act, 3) some people were out, and 4) some houses were uninhabited.

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Our previous research included a social survey in Aichi Prefecture on Post-Disaster Timelines (PDTs), that is, people 's sense of time regarding “what to do” and “when to do it ” in the aftermath of a large-scale disaster. We conducted similar surveys in other prefectures in Japan (Mie and Kochi) and analyzed PDTs in the three prefectures. The results showed that the PDTs in Aichi Prefecture were generally earlier than those in Mie and Kochi prefectures. We also found that Aichi Prefecture had greater differences in PDTs between people in different individual attributions than Mie and Kochi prefectures. The data suggested that the industrial structure of Aichi prefecture, which is closely linked to the overall Japanese economy, affected characteristics of its PDTs. The PDTs of the geographically adjacent Aichi and Mie prefectures were not similar; rather, the PDTs of Mie and Kochi prefectures were similar. These findings suggest the need to take into account characteristics of each prefecture 's PDTs in the recovery and reconstruction process in the event of a wide-area disaster, such as one that spans multiple prefectures.

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In Kazamaura Village, Aomori Prefecture, the possibility of a sediment disaster became very high due to the torrential rainfall in August 2021, and an “evacuation instruction ” was issued for the entire area. In this case, no human victimizations occurred, but since a fatal disaster was fully considered, a questionnaire survey of all households was conducted. And the characteristics of evacuation behavior were clarified, and the potential human victimization caused by sediment disaster was discussed. As a result, residents ' behavior could be classified into four types. In particular, in the “Shimofuro area, ” even if the likelihood of sediment disaster in the future were to become very high, it is highly likely that nearly one-third of residents would not evacuate. Therefore, the likelihood of human victimizations from sediment disaster was evaluated as “very high ”. In the future, disaster prevention education that removes the experience bias of residents is urgently needed.

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Yasuda et al. (2021) reported that the persistence of the effects of the disaster risk reduction (DRR) education was limited in elementary schools in coastal areas; however, prefectural differences (Fukushima and Miyagi) were not analyzed. In this study, we reanalyzed the data of Yasuda et al. (2021) to clarify the differences between the two prefectures. The results showed that children 's disaster awareness prior to the class was higher in coastal areas than in inland areas, with children on the Fukushima coast more willing to learn about disaster prevention and share what they learned with their families. Those on the Miyagi coast were also more aware and confident about evacuation behavior. The Fukushima coastal children 's assessment of the risk of natural disasters further increased one month after the class. Many aspects of disaster awareness also persisted one month after the class for the Miyagi coastal children. The number of discussions and disaster prevention actions taken at home after the class was also higher in the coastal areas than in the inland areas.

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From late in the evening of September 23 to early morning of September 24, 2022, the central part of Shizuoka Prefecture experienced heavy rainfall, and the Shizuoka (Regional Meteorological Observatory) recorded the highest 12-hour precipitation of 404.5 mm in its observation history. The maximum 24-hour rainfall was also the second highest (416.5 mm) after the 508.0 mm observed due to the “ Tanabata heavy rainfall ” in 1974. The heavy rainfall caused outside and inland water flooding in the Tomoe River and its tributaries in Shimizu Ward of Shizuoka City, resulting in almost 5,000 houses being flooded in the city. Based on the inundation depth maps prepared by the authors based on their survey of inundation depths at approximately 1,150 locations, the flood inundation assumption area map (planned scale) and the inundation area were almost identical. The Torisaka, Ouchi and Shibukawa areas recorded a maximum inundation depth of just under 250 cm, but this was less than the depth in 1974. On the other hand, Ouchi, Horigome, Kami areas were flooded with a difference of around 10 cm, which is close to the depth of the “ Tanabata heavy rainfall ”.

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The disaster survivors who independently rebuild their livelihood in reconstruction projects area utilizing governmental reconstruction initiatives can be categorized into four groups: Type I - Reconstruction Fascination, Type II - Elderly Health Concerns, Type III - Community Attachment, and Type IV - Enriched Human Relationships. Types I and III together constitute approximately 86% of the disaster survivors rebuilding their home in the reconstruction project area. Type I indicates the potential to incorporate individuals who chose to independently rebuild in different regions without utilizing such initiatives. Type II emphasizes the importance of mental and physical health, while Type IV highlights the “ abundance of connections with others ” as significant factors in the rebuilding process.

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In recent years, the frequency of floods exceeding the planned magnitude has been increasing in Japan which is forcing society to cope with such increasing external forces. In this study, in order to assess available storage functions in sub-basin scales for class A river systems, existing storage capacity was evaluated by flood control storage of dams as well as hydropower and agricultural water dams, additionally by retarding basins and agricultural ponds, and paddy field storages. As a result, the storage capacity by basin flood control measures was quantified in terms of equivalent rainfall evaluation (mm) storage volume (m³) by catchment area (km²), which is expanded to a nationwide map to make possible to evaluate whole river basins in Japan on the same scale. These outputs can be utilized to enhance river basin flood management such as to select possible new dam sites and so on.

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