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38% of evacuation centers in central Tokyo, 20 major cities in expected flood areas

The Mabicho district of Kurashiki Okayama Prefecture, hit by torrential rain, is seen flooded in this photo taken from a Mainichi Shimbun helicopter on July 8, 2018. (Mainichi/Tadashi Kako)

TOKYO -- As many as 38 percent of current and planned public evacuation centers are located in severe flooding danger areas in the 23 wards of Tokyo and 20 designated cities with a population of 500,000 or more, a Mainichi Shimbun poll of the municipalities has found.

Half of the capital's evacuation centers, especially those in eastern parts of the city below sea level, would be submerged in a flood caused by a one-in-a-millennium-scale rainfall. In the case of Osaka in western Japan, more than 80 percent of such facilities face the risk of flooding if the Yodo and Yamato rivers flooded.

Many of the local governments concerned are trying to devise plans to evacuate their residents further afield, such as to other cities and towns.

Under the Flood Control Act -- revised in 2015 in response to global warming -- cities, wards, towns and villages are required to publicize which areas under their jurisdiction are expected to be submerged in the event of a millennium-level rainfall disaster. The previous standard demanded the public be informed of flood risks connected to rainfall on scales seen every one to two centuries.

By area, 70 percent of evacuation centers in the city of Niigata on the Sea of Japan coast are expected to be submerged due to the flooding of the Shinano and other local rivers in the event of catastrophic rainfall. The same ratio of centers in Kawasaki south of Tokyo would be flooded should the Tama River overflow. Meanwhile, inundations are projected to hit 50 percent of evacuation sites in Kyoto, western Japan, and 40 percent in the cities of Saitama, north of Tokyo, Hamamatsu and Nagoya in central Japan, and Kumamoto in southern Japan.

Among the capital's 23 wards, all designated evacuation centers in Adachi and Katsushika would be flooded. The ratio is more than 90 percent in Arakawa, Edogawa and Sumida, and more than 80 percent for Koto, Taito and Chuo -- mostly in eastern Tokyo.

Flooding of designated evacuation centers posed a serious threat to evacuees during the torrential rains and flooding that hit western Japan in July last year. In the Mabicho area of the city of Kurashiki, Okayama Prefecture, 14 of 22 such facilities were inundated by flooding that that covered 12 square kilometers of the district. Evacuees forced to find shelter outside the flood zone pushed three evacuation centers still running over their operating capacity.

Some municipal governments covered by the latest Mainichi Shimbun survey, including the southern Japan city of Fukuoka, expressed concerns about the challenge of securing evacuation centers that would remain dry even in the case of worst-case rain and flooding.

In preparation for such a devastating flood, the five wards of Sumida, Koto, Adachi, Katsushika and Edogawa in Tokyo have introduced a procedure to advise residents to leave those areas nine to 24 hours before the arrival of massive storm surges due to a typhoon or flooding of rivers. The local governments also advise residents to secure locations where they can flee in advance, such as relatives' homes.

However, natural disasters are not limited to flooding. Western Japan municipalities face the possibility of being hit by a massive Nankai Trough earthquake, which could cause as many as 820,000 people to evacuate in the city of Osaka alone. This far exceeds the upper limit of some 600,000 people the city's 546 evacuation centers can accommodate.

Moreover, projected flood areas due to a quake-induced tsunami are estimated to be different from those due to river overflows and other causes, making it difficult for municipal officials to devise wide-area evacuation plans for residents.

"We want to have a broad-area evacuation plan, but there are many challenges to overcome to secure evacuation centers," said an Osaka city official in charge. The official said the process to devise such a plan can be complex because flood risks posed by a tsunami must cover coastal areas, while river overflows would endanger areas along the banks.

(Japanese original by Motohiro Inoue, Kobe Bureau)

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