TOKYO -- Many residents in areas flooded by Typhoon Hagibis failed to use local hazard maps to consider evacuating because they didn't know they existed, an issue which was compounded by the fact that the spread of water was almost identical to the maps' projections.
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In response to the revelation, experts urged local bodies to consider more effective ways to distribute information about hazard maps, and for residents to make good use of them to devise evacuation plans in anticipation of flooding.
Wide areas of the central Japan city of Nagano were flooded after an embankment of the Chikuma River burst after it was swollen by rains from Typhoon Hagibis over Oct. 12 and Oct. 13. Predicted flood areas in a hazard map recently compiled by the Nagano Municipal Government corresponded almost exactly with the locations that actually flooded.
The map, which also indicates evacuation shelter locations, is based on a scenario in which an average of 396 millimeters of rain falls over a two-day period, an event said to occur once every 1,000 years. This summer, the city distributed the map to all households in areas of the city that it believes could flood.
Estimates released by Japan's Geospatial Information Authority of areas that did flood in the latest typhoon matched hazard map predictions that the west bank of the Chikuma River, where the embankment broke, would flood. The Nagano bullet train depot where many Hokuriku Shinkansen Line trains were swamped by flood water is also situated in an area that the map estimated would see the deepest level of inundation.
The preliminary figure for average rainfall near where the river burst over the two-day period is 186.6 millimeters, roughly half the amount used to make the map. Had rainfall been greater, the damage could have been even more serious.
Eiichi Shibata, 66, a former leader of a neighborhood association in the Hoyasu area where the break occurred, knew about the hazard map. Evacuation orders were issued to his neighborhood at 11:40 p.m. on Oct. 12. Moreover, the river's water level at a nearby observation point surpassed the designated alarm level that could have triggered a flood by midnight.
At around 1 a.m., Shibata fled to a nearby evacuation shelter with his 97-year-old mother. His home was flooded above floor level, but nobody in his family was injured. However, two people in the city lost their lives.
Shibata stressed the need for people to check their neighborhood hazard maps, "Unless you look at the map, you won't know where you should take shelter. I've come to appreciate their importance," he said.
In Marumori in Miyagi Prefecture, northeastern Japan, the areas which flooded after embankments at two branches of the Abukuma River burst were also largely identical to the anticipated flooding on the town's hazard map. However, the way in which these areas were submerged differed slightly from the hazard map's projections.
The municipal government believed the northern part of the town could suffer particularly serious damage on the basis that defenses on the Abukuma River's north bank were likely to burst. The river runs through the northern and central part of town where the municipal government building is located. It was assumed that flood water in residential areas could reach 3 to 5 meters deep.
But in the actual disaster, levees at the Abukuma River remained intact, while dikes broke near where two branches of the Abukuma River -- the Shinkawa and Uchikawa rivers -- meet. They converge at a point near the central part of town. In addition to floodwaters from the rivers, a massive amount of water also flowed into the center of the town from a nearby mountainside. The deluge that rushed into areas far surpassed the capacity of town drainage pumps, causing water to overflow from ditches and pipes, thereby flooding most of the town's central area.
At 7:50 p.m. on Oct. 12, the highest-level of disaster warning was issued to the entire town, and the local government urged residents to evacuate. But some people failed to escape in time because they did not know they were under threat as described by the hazard map.
"I didn't know there was a map. I was home that day. When water rose to the second-floor staircase I was scared," said a 58-year-old woman. "If I had known about the hazard map, I might have done things differently."
The disaster claimed the lives of many residents of Marumori, and left others missing. But the majority of them are concentrated in mountainous areas surrounding the town. Many of them were apparently caught in landslides.
The municipal government had anticipated that heavy rain from the typhoon could trigger landslides. However, it assumed that such a disaster would occur after ground became fragile from being inundated with massive amounts of rain. An official said town authorities had not expected landslides would be caused by volumes of rain falling on a single day.
"We want to keep residents informed of hazard maps. However, disasters don't necessarily take place just as we assume. The map alone isn't enough to ensure residents are fully aware of the risks from disasters. We must also consider other ways to inform them," said a municipal government official in charge of disaster management.
(Japanese original by Kunihiro Iwasaki and Ryotaro Ikawa, City News Department, Masaru Yoshida and Hana Fujita, Sendai Bureau)