The 2021 Nishinomiya wildfire was one of the largest cases in Japan, which occurred from 21 Feb. 2021 with 167 ha as a burnt area. There are two features in this event. The first was dried condition with a strong local wind. When the local wind, Akagi Oroshi, hit the area on 23 and 24 Feb., the fire spread drastically. The second was that a large-scale fire broke out near the residential area, which significantly impacted the surrounding area. In the fire severity survey, the stem bark char heights were measured at 113 points in the area. The severity in the trees was mainly low, indicating that even in this large-scale case, under dry and windy conditions, the form of fire spread was surface fire, with limited trunk fire and no crown fire in this event, where the dominant combustibles were on forest floor.

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Disaster information collecting dissemination using SNS in the event of a disaster has become active in practical and academic discussions since occurring the 2011 Great East Japan Earthquake in Japan. In this paper, we investigated the recent situation regarding SNS usage trends of disaster survivors and clarified the features and issues. The main results are as follows. 1) Even 10 years after the 2011 Japan disaster, about 70-80% of TVs and about 40-60% of radios were the main means of collecting information in the disasters. LINE and Twitter as SNS tools have become the main collecting media following TV and radio, accounting for about 20-40%. 2) Only about 20% of the survivors send information using SNS in the disasters. The transmission is mainly done by LINE. 3) About 30% of the survivors had the experience of receiving troublesome information from SNS during disasters. The information that was particularly troublesome was not factual information, but incorrect information (including hoaxes), received information that caused anxiety, and too much information, making it difficult to determine the necessary information. That was, the information was updated remarkably, and they saw information that had nothing to do with the disaster.

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In Ajiro, Atami City, in Shizuoka Prefecture, Japan, Baiu-front stagnated from July 1 through July 3, 2021, and 48 hours precipitation resulted in 321.0 mm (return period : 23 years) of precipitation. On July 3rd at 10:55 a.m., a large-scale debris flow caused the collapse of the embanked ground on the Aizome River in the Izusan District, resulting in at least 27 deaths and/or missing persons (As of October 28). The writer surveyed 141 heavily damaged buildings. This district is designated as collapse special caution area of steep slopes (Red zone), collapse caution area of steep slopes (Yellow zone), and debris flow caution area (Yellow zone), and a land condition figure presents this district’s topography as “debris flow deposits.” The precursory phenomenon was confirmed in this debris flow disaster, but since only elderly people had been advised to evacuate from Atami City, there were no inhabitants who relocated to the evacuation site beforehand.

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In 2021, from August 11th to the 14th, the autumnal rain front developed with continuous rainfall, and an area of heavy precipitation was observed with a period maximum measurement of 1,000 mm in the east-to-west direction of Higashisonogi in Nagasaki Prefecture to the Chikugo area of Fukuoka Prefecture. The daily precipitation measurement in Ureshino Amedasu on August 14th was 439.5 mm with a return period of about 600 years, showing an extremely rare precipitation phenomenon. The water level of the Rokkaku River at the Shiomi Bridge point exceeded the estimated high-water level of 4.00 m before the three o’clock on the same date and continued to exceed the level for six-and-a-half hours, with maximum level of 4.85 m by seven o’clock. Due to the high water level, the drainage pumping stations in seven locations were not fully operated for a total of eight-and-a-half hours; however, they were not able to drain the rainwater in the floodplain of the Rokkaku River, resulting in the flood inundation. In the Asahicho district of Takeo city, the maximum flood depth was 160 cm, and this level was equivalent to the flood disaster in 2019; however, the measurement exceeded over the 200 cm in many locations at Tachibanacho, and the level surpassed the 2019 flood level by maximum of over 1 m. In Kitakatamachi and Omachicho, peak flood depths exceeding 2019 levels were also observed.

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