2018 Japan floods

Date: June-July 2018

Place: Southwestern Japan, primarily the Hiroshima and Okayama regions.

Result: Tropical moisture and a stalled weather front combined to dump torrential rains on the region over a two-week period, causing widespread flooding and mudslides. More than 225 people were killed, making it the deadliest flooding event in Japan since the early 1980s.

Overview

The 2018 Japan floods were a series of devastating floods that took place after Japan received record-breaking amounts of rain during a single season. The remnants of a typhoon combined with strong thunderstorms to drastically increase the amount of precipitation received by the country in during late June and early July. This resulted in severe flooding in several Japanese regions, principally Hiroshima and Okayama. Flooding in those regions caused extensive property damage and left at least 225 people dead. A large amount of the damage was the result of mudslides caused by the floods.

Floods occur when water temporarily overflows onto land that is normally dry. Some floods develop slowly, when water levels in rivers, streams, and other bodies of water gradually rise over a season. Other floods occur rapidly, when bodies of water suddenly rise and overflow their banks. Floods commonly result from powerful coastal storms, such as hurricanes and typhoons. These storms can dump large amounts of rain on a small area in a brief period of time, causing rapid flooding.

The nation of Japan consists of several islands in the North Pacific Ocean. Its location and geography makes it a prime target for typhoons. Typhoons are rotating tropical storm systems that can carry large amounts of moisture and potentially devastating winds. They are referred to as hurricanes in the Atlantic Ocean.

While Japan has a higher-than-normal risk of flooding, unusual weather patterns during June 2018 created the conditions that led to record-breaking rainfall. A stationary weather front stalled over Japan, bringing with it days of rain. The situation was made worse when tropical moisture from the remains of Typhoon Prapiroon streamed north and collided with the front. Prapiroon was a category 1 typhoon that passed between southern Japan and South Korea on July 3 before weakening to a tropical storm and eventually, a low-pressure system. The system was laden with moisture from the warm waters of the Pacific and combined with the stalled front to inundate Japan with rain.

Southwestern Japan received record breaking amounts of rain. Many areas received more than 39 inches of rain over several days. Some isolated areas of Japan were hit with up to 70 inches (178 centimeters) of rain over a two-week period. By July 5, rivers and streams in southwestern Japan began to overflow their banks. Emergency warnings were issued for several prefectures, including Okayama, Hiroshima, Tottori, Fukuoka, Saga, Nagasaki, Hyogo, and Kyoto. Japanese disaster management officials described rainfall amounts as the worst they have ever experienced. Floodwaters reached as high as 16 feet (4.9 meters) in the hardest-hit areas.

The days of soaking rain also weakened the earth in mountainous areas, resulting in severe mudslides. The area around Hiroshima alone reported more than 1,200 mudslides, more than the average number in Japan over the course of a year. The rains began to subside by July 9, but the country was then hit with a major heatwave as temperatures soared to near 90 degrees Fahrenheit (32 Celsius).

More than 8 million people were forced to evacuate their homes either from the flooding or from the damage caused by mudslides. In some cases, flooding and property damage hampered evacuation efforts. In these scenarios, rescue crews were utilized to evacuate citizens in dangerous areas. More than seventy five thousand response staff were utilized to help rescue stranded Japanese citizens.

Impact

The two regions most damaged by the storms were the Okayama and Hiroshima prefectures. However, the Saga, Fukuoka, Yamaguchi, Ehime, Kochi, Hyogo, Kyoto, Shiga, and Gifu prefectures also sustained significant damage. Much of the damage came from rivers overflowing their banks, but significant damage was also caused by mudslides. The total cost of the devastation was estimated at between $2.6 billion and $4 billion US dollars. At least 225 people were killed in the flooding. This was the highest death toll for a non-tsunami flooding event in Japan since 1982.

Many experts argued that Japan was not adequately prepared to deal with the flooding, which may have contributed to the large numbers of lives lost. Though experts had mapped out areas that were at significant risk for flooding, homes and businesses had already been built throughout many of these regions. Additionally, though early warning tools were in place, many residents thought that they were given warning of the severity of the incoming storms too late to effectively evacuate. This may have resulted in people trapped who otherwise could have evacuated.

Several conditions contributed to the unusual devastation caused by the 2018 flooding. Most communities in Japan have been required to create hazard maps, assessing the risk of damages from floods and mudslides in specific areas. However, many homes and businesses were constructed in these areas before the hazard maps were drafted. For this reason, numerous structures were built in areas at high risk of damage from flooding and landslides.

Some experts argued that despite the existence of hazard maps, knowledge of the areas that were at higher risk for damage was not widespread enough. Some residents complained that they were not aware that they lived in a designated risk area. Many of these areas were badly damaged during the 2018 flooding.

Many of the victims of the flooding were warned to evacuate in advance. However, many argue that they did not have enough time to properly evacuate after warnings were given. Though complex electronic systems can be used to predict weather, sometimes rapidly developing storms still result in short notice. Additionally, some Japanese citizens refused to evacuate their homes, choosing instead to attempt to stay through the storms.

Bibliography

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