This study aims to clarify the relationship between roof snow accidents and meteorological factors in Toyama Prefecture based on previous studies in Yamagata Prefecture. First, we used the daily maximum temperature and seven-day snowfall to analyze the relationship between these factors and the number of accidents. In the relationship between the number of accidents and the maximum daily temperature, as in the previous study in Yamagata Prefecture, the number of accidents increased when the maximum daily temperature was a few degrees Celsius. In addition, the relationship between the number of accidents and the amount of snowfall over seven days showed that more accidents occurred when the amount of snowfall was higher. In Toyama Prefecture, most accidents were fall accidents, suggesting that human factors caused several accidents due to the increased need to remove snow. Advisory criteria were developed using the daily maximum temperature and the amount of snowfall over seven days to determine the risk of an accident occurring under certain weather conditions. The advisory criteria were validated using validation indices. Overall, roof snow accidents occurred, although the number of accidents was lower than that in previous studies. The fact that human factors, such as the necessity of removing snow, are stronger than meteorological factors, such as temperature and snowfall, which suggests that accidents can be prevented by human awareness and that it is crucial to raise awareness.

Laboratory experiments were carried out with natural seawater that was frozen in a tank at －25 ℃ in a low-temperature room to understand the factors controlling the precipitation of ikaite (CaCO₃・6H₂O) crystals in sea ice. The seawater remained frozen for 1, 7, or 21 days and was then melted at ＋4 ℃．Measurements of the numbers and sizes of ikaite crystals revealed no ikaite crystals after one day of freezing, but there were 565 and 4998 crystals per liter of seawater after 7 and 21 days of freezing, respectively. The distribution of crystal sizes depended on the duration of freezing. We examined the effect of changing the carbonate chemical components of the seawater on the precipitation of ikaite crystals by adding NaOH to the natural seawater prior to freezing. The number of ikaite crystals increased with increasing amounts of added NaOH because conditions became more favorable for precipitation of ikaite crystals at high pH.

We constructed and analyzed a database of vehicle-stranding events due to snow to investigate the occurrence characteristics of vehicle-stranding events caused by snowfall in Japan. The database was constructed by collecting data from road administrator's reports, online news reports, and reports posted on Twitter from public and media organizations. As a result, 423 events that occurred between January 1986 and April 2021 were compiled in the database. The characteristics of the events were analyzed by focusing on eight items, namely the yearly number of events, area of occurrence, road classification, month of occurrence, time of occurrence, cause of occurrence, type of vehicle that triggered the event, and scale of the event. The results show that vehicle-stranding events have been occurring increasingly in recent years; the Hokuriku region has the largest number of vehicle-stranding events, but there are events in 40 prefectures including non-snowy areas; many events occur during the daytime, while there are fewer events in the early morning and late evening; and most events are caused by vehicles getting stuck on compacted-snow road, but in Hokkaido, which is a cold region, most events are due to low visibility and snow drifts. Furthermore, it was found that most large-scale events after 2010 occurred on national expressways and national highways in the Hokuriku and Sanin regions and in non-snowy areas, and were triggered by large vehicles getting stuck on compacted-snow road.