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Lack of inland flooding maps in Japan areas hit by 2011 tsunami: Mainichi survey

Ishinomaki in Iwate Prefecture is seen inundated with water that is believed to have been brought in by inland flooding caused by Typhoon Hagibis in 2019, in this image taken by a resident and sent to the Tohoku University International Research Institute of Disaster Science, which supplied the image.

Among 37 coastal municipalities in the prefectures of Iwate, Miyagi and Fukushima hit by the tsunami brought by the Great East Japan Earthquake in March 2011, over 80%, or 31 municipalities, have not drawn up hazard maps showing potentially dangerous areas in the event that heavy rains cause inland flooding from overwhelmed drainage systems.

When powerful Typhoon Hagibis passed through northern Japan in October 2019, inland flooding occurred in some areas that have been subject to reconstruction including having embankments built. It's believed that the presence of the structures was one of the causes for the flooding, in which water rises from the ground and waterways as opposed to overflowing from the river itself.

Many municipalities that were affected by the tsunami have focused their efforts on infrastructure that will mitigate damage from the next huge wave. But the increased prevalence of heavy rains that has come with climate change now means that they must do more to tackle inland flooding, too.

In the town of Yamada in the northeastern prefecture of Iwate, 81 residences in an area of some 65,000 square meters were flooded following damage by Typhoon Hagibis in autumn 2019. The area was near embankments built to prevent tsunami damage.

It appears the flooding was caused by mountain earth falling in landslides and clogging up drainage pipes. This is thought to have led to the embankments acting like walls stopping up the flow of wastewater. Additionally, in the city of Ishinomaki in neighboring Miyagi Prefecture, rainfall exceeded predicted amounts, and temporary pumps stopped working, resulting in the flooding of 244 residences in the area classed as replacement housing.

A resident of Yamada, Iwate Prefecture, is seen cleaning her home of floodwater caused by inland flooding, on Feb. 27, 2020. (Mainichi/Maika Hyuga)

In January and February, the Mainichi Shimbun sent out a questionnaire to 37 municipal authorities in the three prefectures that included queries such as whether they had drawn up hazard maps for inland flooding. All 37 responded.

Thirty-one municipalities, including flood-hit Yamada and Ishinomaki, reported that they had not put together such hazard maps. The survey included multiple choice sections to explain why. Nine municipalities said they had not done so because creating the map would cost a large amount of money, eight said they would be turning their attention to it after work to repair and rebuild infrastructure damaged in the earthquake was done, and another five said that historically they hadn't suffered great damage from floods.

The results showed that for many areas that were affected by the 2011 tragedy, their efforts to prevent disasters have been concentrated on earthquakes, leading to a slowdown in preparation against other potential issues such as flooding.

Six municipalities said they were creating inland flooding maps. They were the city of Kuji and the village of Tanohata in Iwate Prefecture, the town of Watari and the cities of Shiogama and Sendai in Miyagi Prefecture, and the city of Iwaki in Fukushima Prefecture.

Four have decided on a timetable to create inland flooding hazard maps: the city of Miyako in Iwate Prefecture, the city of Ishinomaki and the town of Onagawa in Miyagi Prefecture, and the town of Shinchi in Fukushima Prefecture. Among the reasons for why, officials at Miyako said that the inland flooding experienced during Typhoon Hagibis has spurred them to create a hazard map.

The remaining 27 municipalities have yet to finalize plans for hazard maps, but there were many looking into creating them, with the Miyagi Prefecture city of Higashimatsushima and others saying they would turn to the work once they had finished repairing and rebuilding infrastructure damaged in the earthquake in March 2011.

According to the Ministry of Land, Infrastructure, Transport and Tourism, among 484 municipalities that have in the past experienced significant damage from inland flooding and for whom it is necessary to create hazard maps, a quarter of them, 123 municipalities, had not made or announced any by the end of fiscal 2018.

Among the 27 municipalities affected by the disaster in Iwate, Miyagi and Fukushima prefectures, 14 of them, around half, have yet to draw up or announce any hazard maps. Even when compared to national rates for the drafting of such maps, progress appears to have stalled in these areas.

(Japanese original by Nobuyuki Hyakutake, Ishinomaki Local Bureau; Maika Hyuga, Morioka Bureau; and Ikuko Ando, City News Department)

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