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Hiroshima Pref. survey to ask residents why they didn't evacuate in deadly downpours

An area in Aki Ward of the city of Hiroshima is flooded on July 7, 2018 during recent torrential rains that devastated western Japan. (Mainichi)

HIROSHIMA -- The Hiroshima Prefectural Government will begin a survey as early as this fall to find out why some residents did not evacuate during deadly torrential rain this summer that killed 108 people in the prefecture and 100 more in other western Japan prefectures, officials have disclosed.

The prefecture intends to compile the results of the survey -- the first of its kind to be carried out by a local government -- by the end of current fiscal year ending March 2019 at the earliest so that the information can be used to reduce damage caused by such natural disasters.

The decision to carry out the study is based on the finding that 41 of 87 people killed in landslides during the downpours -- almost half of the victims -- died in areas where such natural disasters had been anticipated. Municipal governments were obligated to distribute hazard maps showing areas that were expected be hit by landslides, and had released areas to be designated as being at high risk, so residents were assumed to have known the dangers they faced to a certain extent.

Another factor prompting the prefecture to conduct the survey is the fact that a vast majority of residents chose to stay home despite instructions from the authorities to evacuate. Of a total of 2,169,609 residents who became subject to evacuation orders, 5,788, or only 0.3 percent, actually moved to evacuation centers between 7:40 p.m. on July 6, when the Japan Meteorological Agency issued an emergency torrential rain warning, and 10:30 p.m., when all affected local municipal governments had issued evacuation instructions.

The prefecture experienced massive landslides in 2014 that killed 77 people, and has since focused its countermeasures on improving physical protection, such as building erosion control dams and other facilities, as well as designating areas facing a high risk of landslide damage. With the latest torrential rains this summer and its large human cost, prefectural officials decided to review their current stance and pay more attention to residents' mindset when they experience major natural disasters.

The upcoming survey will try to find out why some people evacuated and others didn't in the same areas that suffered major damage by asking them the reasons for their actions during the downpours. The prefecture will also review how evacuation orders and relevant instructions were issued by municipalities in a bid to better understand ways of providing information that will result in actual evacuations. The city of Hiroshima will set up a panel of experts to examine people's actions of evacuating or staying put during the torrential rains.

According to the prefecture, the survey will be the first large-scale study on evacuation actions during a natural disaster by a local government. No such survey was conducted in areas affected by the Great East Japan Earthquake in 2011 or the Kumamoto earthquake in southern Japan in 2016.

A prefectural official said, "We want to review our response in the latest disaster using behavioral psychology, and to find out effective ways to make people aware of the dangers and evacuate."

Professor emeritus Hirotada Hirose of Tokyo Women's University, a specialist in disaster risk studies, conjectured that people do not evacuate quickly enough because in some cases they are influenced by "normalcy bias." This is a mindset people try to stay calm by underestimating emergencies without overreacting to changes, according to Hirose. It is possible that some people relied on their experiences in past incidences of torrential rain that did not result in major disasters, and accordingly did not evacuate, he added. "Based on the results of the upcoming survey, the authorities should think about ways to persuade residents to evacuate."

(Japanese original by Itsuo Tokubo and Misa Koyama, Hiroshima Bureau)

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