Western Japanese Floods

First Posting | Summary
Posting Date: July 12, 2018, 6:00:00 PM

Several days of record-breaking rainfall between July 4 and 8 led to widespread inland flooding in 11 prefectures across western and central Japan. The precipitation was described by an official at the Japan Meteorological Agency (JMA) as being “at a level we have never experienced.” As well as numerous rivers and streams bursting their banks, many landslides have been reported. In addition to major damage to buildings and infrastructure, there has been considerable business interruption. At least 180 lives have been lost, and dozens are unaccounted for, according to data issued on July 12 from the Fire and Disaster Management Agency (FDMA). This is Japan’s deadliest flood since 1982 and the country’s deadliest natural catastrophe since the 2011 Tohoku earthquake. Search and rescue operations by the government have deployed more than 70,000 emergency personnel.

Meteorological Summary

The precipitation began on July 4 as a seasonal “Baiu” rain front that interacted with moisture from the remnants of Typhoon Prapiroon, which dissipated over the Sea of Japan on that day. The front continued to drench already saturated soils until July 8. The JMA issued an Emergency Heavy Rain Warning for Tottori, Okayama, Hiroshima, Fukuoka, Saga, and Nagasaki prefectures—a level of warning used only when an amount of rainfall not seen for decades is anticipated. 

In just a few days, parts of Japan received four times the rainfall typically expected in the whole month of July, according to the JMA. Many locations set records for heaviest rainfall during a 24-hour, 48-hour, and 72-hour period. In Kochi Prefecture, for example, 1,190 mm (46.85 inches) of rain was recorded unofficially in Umaji village in a 72-hour period, with unofficial totals from the World Meteorological Organization (WMO) ranging from that 1,190 mm up to 1,852 mm (72.91 inches) in Yanase. In Shikoku Island’s town of Motoyama, rain totals of nearly 583 mm (23 inches) fell between the morning of Friday, July 6, and the morning of Saturday, July 7. JMA data indicates that 15 station gauges recorded at least 1,035 mm (40.75 inches) of rain falling between June 28 and July 8. According to media reports, new rainfall records were set in 93 locations.

Numerous rivers in the impacted regions crested above their historic levels. Floodwaters reached as high as 5 meters (16.4 feet) above normal levels in many locations, and watercourses across the region overflowed. Several rivers such as Asahigawa, Takahashi, Misasa, and Houmangawa rivers near the cities of Okayama, Kusashiki, Hiroshima, and Fukuoka, respectively, experienced over 500-year return period flows. The Hijikawa River in Ehime Prefecture overflowed with an over 250-year return period flow.

The rainfall abated on Monday and water levels began to recede in some areas, but railroads and highways remained closed in affected regions, hindering relief and rescue operations. With soils saturated, there is a continued risk of landslides occurring.

Exposure at Risk  

Residential exposures in Japan are dominated by wood construction, with non-wood residences primarily consisting of steel and concrete. Most of the single-family building stock is two stories built with wood stud walls as well as concrete footing and foundations less susceptible to flooding. Concrete is also often used in buildings taller than two stories. Apartment complexes in Japan are usually of steel construction. The commercial and small industrial building stock in Japan uses a wider variety of construction materials than residential buildings.

The vulnerability of buildings to flood damage varies by construction and occupancy types. For a given flood depth, a residential concrete building is expected to withstand more than a residential wood-frame building. Steel construction is similar to concrete. Flood damage to buildings is usually confined to nonstructural components, such as electrical equipment, fixtures, and fittings; water damage to machinery and contents drives most flood loss. Large apartment or condo complexes, which are typically steel construction, have a higher level of engineering than single-family homes but are still very vulnerable to flooding, as the cost of damageable components such as equipment is higher for large condos.

Reported Damage and Disruption

More than 8 million people from 23 prefectures in western and central Japan have been ordered to evacuate; thousands of them are living in gymnasiums, schools, and other temporary shelters. In addition, 71,000 dwellings have been set up as temporary housing, according to a statement made by Prime Minister Shinzo Abe during his visit to a shelter on July 11 in Okayama. Abe plans to visit Ehime Prefecture on July 13. 

More than 23,000 residential buildings have been destroyed or damaged, according to data issued on July 12 from the Fire and Disaster Management Agency (FDMA). Many vehicles have been swept away and large areas are choked with mud and debris. As the full scale of the devastation becomes apparent, however, estimates of the damage experienced are likely to rise

Rail services across western and central Japan, among them the Shinkansen bullet train, were suspended because of debris on the rails or track being washed away. According to Japan's transport ministry, 27 train lines have experienced damage—mostly from landslides—at more than 100 locations. It is not clear when rail service on these lines will resume. After its workers evacuated it on Friday, the Asahi Aluminium Industrial Company’s plant in Okayama exploded. Across the region roads, bridges, and other infrastructure are reported severely damaged or destroyed.

Thousands of homes have lost electricity, many phone lines were downed, and roughly 270,000 homes have lost their water supplies. Daily temperatures reaching higher than 30°C (86°F) and high humidity are exacerbating the situation. Access to food is also a concern, as it is unclear whether people can travel to and from supermarkets safely and whether supermarkets have much food in stock. Aid and supplies are arriving in affected areas, but distribution is a challenge.

There will inevitably be widespread business interruption, particularly to auto and electronics manufacturers; impacted companies include Mazda, Panasonic, Daihatsu, and Mitsubishi. Production has been suspended at several plants because of supply chain disruption, but no damage to facilities is reported. Oil terminals and refineries are said not to be impacted.

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Posting Date: July 12, 2018, 6:00:00 PM

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