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Hiroshima landslide survivor, expert say dissemination of risk data insufficient

The Umego housing development in Hiroshima's Aki Ward lies devastated by a massive landslide on July 12, 2018, six days after the disaster. (Mainichi)

HIROSHIMA -- Twelve residents at a housing development in the mountains here remain either dead or missing following a massive landslide triggered by the latest historic torrential rains that devastated a wide swath of western Japan -- and some suggest fatalities could have been averted had authorities made more efforts to inform residents of landslide risks.

On May 17, about seven weeks before the deadly landslide, the Hiroshima Prefectural Government released a risk assessment map alerting residents of the Umego housing development in the Yanohigashi district of Hiroshima's Aki Ward about a potential landslide. The prefecture planned to designate part of the development as a "landslide disaster special alert area" following an explanatory meeting with local residents to be held in August.

The designation means landslides in the area pose a significant risk to the lives of local residents. It was to be introduced based on lessons learned from a massive August 2014 landslide in the north of the city of Hiroshima including Asaminami Ward that killed 77 people. The prefectural government released the risk assessment map before official designation of the alert area in response to a legal change after the 2014 disaster that made it mandatory to release completed maps immediately.

Even so, the lessons from the 2014 landslides and the warning based on them, apparently were not enough to save the victims of the latest disaster. A huge stream of mud and rocks swept away many houses in the development on the night of July 6. The direction the deadly flow took was similar to that predicted in the risk assessment map.

On July 12, the Umego housing development, which opened more than 20 years ago, was buzzing all day with the deep sounds of heavy earth-moving equipment removing landslide debris. Many victims who escaped alive are now staying in evacuation centers, and few people can be seen on the grid of streets. Trees and rocks rest where houses used to stand, and furniture and picture albums lie in mud.

"If only the risk information had reached people," said Kenji Kakehashi, 74, suggesting that authorities should have done more to alert residents. His house was spared by the landslide, but a former colleague at a car factory, 69, and his wife, 66, remain missing after their house, located on the upper side of the slope where the development is situated, was swept away from its foundations.

The couple's house was to be designated as part of a landslide disaster special alert area. It is not clear if they knew of the risks. But in February, when an erosion control dam was installed about 100 meters above their place, the man said that he felt "relieved," according to Kakehashi. "The end result could have been different had he received an explanation about the designation," Kakehashi lamented. "It's too late now."

Following the deadly 2014 landslide, it was pointed out that one of the factors behind the massive loss of life was that landslide risk designation had not gone smoothly and thus residents were not well informed of the potential dangers. This recognition prompted the legal change that made it mandatory to release the results of landslide risk assessments when surveys to determine the dangers are completed. Some 379,000 areas nationwide were designated as special alert areas as of March this year.

The Hiroshima Prefectural Government released the risk assessment map for the Umego development on its website in May, but locating the information is no easy task from the site's top page. "We intended to release the information early, and worked hard to get it done," said Nobuhiro Furukawa, an official in charge of promoting landslide risk designation, with apparent disappointment.

Another major issue that emerged from the 2014 disaster was the timing of the evacuation advisory. It was issued past 4 a.m., after the landslide occurred. It was said at the time that making the call was made difficult because of heavy rains falling in the wee hours of that day. A committee of experts examining the city of Hiroshima's response to the disaster concluded in January 2015, "It was unavoidable, but it was not appropriate, either." The experts stopped short of clarifying the right time to issue an advisory.

In the latest disaster, it was at 2:18 p.m. on July 6 that the municipal government issued an information bulletin for the whole of Aki Ward to prepare for evacuation and start the transfer of the elderly. An evacuation advisory was then issued at 6:05 p.m., and reports of disaster started to pour in from the district where the Umego housing development is located at around 6:50 p.m. The neighbor of the elderly couple whose house was swept away testified that the landslide hit "around 8 p.m."

The evacuation order came at 8:17 p.m. By then the couple's house was possibly already gone.

Professor Masahiro Kaibori of Hiroshima University, a specialist in sand erosion control who observed the affected district from a helicopter on July 11, emphasized that the accumulated rainfall in the area from the start of the latest downpour was double the amount recorded during the 2014 disaster. "Hazard maps and erosion control dams are designed to work under certain conditions. You have to understand that the reality sometimes exceeds those conditions," said Kaibori. "And you must be ready to act accordingly under such circumstances."

The professor advised that in those cases people must evacuate early "because erosion control dams alone cannot save lives and you should not place too much trust in them."

Kaibori also said that people's action to evade disaster can change if they are aware of the risks, lamenting the fact that the Umego couple could have been hit by the landslide before the risk designation was made.

(Japanese original by Tetsuro Hatakeyama and Ryuo Watanabe, Osaka Science & Environment News Department, and Yukiko Hayashi, Osaka City News Department)

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