The national government requires municipal governments to create and release color-coded hazard maps that notify residents in Japan of levels of flood risks in their local areas.
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It has emerged that in several regions such hazard maps turned out to have almost perfectly predicted areas that were actually inundated following torrential rains brought by Typhoon Hagibis.
A flood hazard map for the central Japan city of Nagano is one such example. In the city, 10 bullet trains at a JR depot for the Hokuriku Shinkansen Line were submerged in water to at least a depth of 4 meters after the Chikuma River breached its banks. While the area was predicted to be inundated to a depth of around 10 meters in the event of flooding, the forecast was apparently not utilized in the latest disaster.
In residential areas in Fukushima Prefecture in northeastern Japan, many people lost their lives after the Abukuma River and other rivers overflowed, even though possible flooding of those waterways had been predicted. There may have been lives that could have been saved if local governments had strived more to expand understanding of hazard maps among local residents.
Almost all municipal governments across the country that are required to create hazard maps have done so. However, such maps were not utilized in disasters in many cases because their contents had not been sufficiently known to local residents.
In the Mabicho district of Kurashiki, Okayama Prefecture, in western Japan, where 51 residents died due to torrential downpours that hit wide areas in western Japan last year, the actual inundated areas almost matched those in a hazard map. However, a post-disaster survey by the prefectural government found that just a little over 20% of households in the area had been aware of the content of the hazard map.
Many local governments carry their hazard maps on their websites, while some bodies distribute printed maps to all households when they are created or updated.
Nevertheless, hazard maps have not been sufficiently recognized by local residents, partly due to their typical mindset of not paying attention to natural disasters until they actually threaten them. There are also people who say hazard maps are too complicated for them to understand.
Local authorities should not wrap up their efforts just by releasing and distributing hazard maps to local residents.
Some local governments informed residents of imminent flood danger via the free communication app LINE by intermittently releasing the rising levels of rivers and other information based on their hazard maps as Typhoon Hagibis swept through the country. Such direct information-sharing is effective and useful.
Compared to earthquakes and volcanic eruptions, the times and locations of possible damage from torrential downpours triggered by typhoons are much more predictable. At a press conference on the day before Typhoon Hagibis approached the country, the Japan Meteorological Agency referred to the possibility of issuing a special emergency warning for heavy rain. Local bodies are urged to ask residents to check hazard maps at an early stage.
Damage from typhoons could be mitigated by disseminating hazard maps to local residents. Authorities are urged to continue persistent efforts to have their hazard maps utilized in the best way possible.