The record-setting heavy rain brought by Typhoon No. 19 caused many rivers to overflow in a short period of time mainly in eastern Japan, resulting in widespread flooding in river basins. With torrential rainfall occurring more frequently in recent years due to climate change, measures such as building levees and dams can only go so far. To save lives, it is essential that residents become more aware of the need to evacuate early.
There are more than 35,000 rivers in Japan. The government has long worked to construct levees and dams to prevent flooding. The cost of flood control projects in the late 1970s was about 360 billion yen a year, but it swelled to about 1 trillion yen a year in the Heisei era (1989-2019), and about 850 billion yen was included in the initial budget for this fiscal year. There are 561 dams for flood control and the total length of embankments is 9,100 kilometers.
However, floods that exceed the government's expectations have occurred frequently in recent years. Starting with the torrential rains that hit western Japan in 2018 and killed more than 280 people (including related deaths), heavy rains such as in northern Kyushu in 2017 and the Kanto and Tohoku regions in 2015 have seen rivers flood regardless of size and caused many deaths.
According to the Japan Meteorological Agency, rainfall of "400 millimeters or more in a 24-hour period" was observed 251 times across the nation from 1999 to 2018. This level of rainfall is likely to cause floods and sediment disasters. The prior two decades saw less than half that number at 121.
During Typhoon No. 19, 102 sites in 18 prefectures recorded record rainfall in a 24-hour period, including the town of Hakone, Kanagawa Prefecture, which recorded 942.5 millimeters over 24 hours.
During both Typhoon No. 19 and the torrential rains in western Japan, dams to protect watersheds from flooding were unable to withstand heavy rains, resulting in emergency releases. "The speed of maintenance has not caught up with the increasing severity of heavy rains," said a Land, Infrastructure, Transport and Tourism ministry official.
The average temperature in Japan has risen by 1.21 C per 100 years due to global warming, and the amount of rainfall is expected to increase as rainclouds become more likely to develop. In addition to levees and dams, "soft measures" that involve raising people's awareness are necessary.
The Japan Meteorological Agency has developed a "risk distribution" map that indicates the likelihood of floods, inundation and sediment disasters in 5 stages based on current information. The system is updated every 10 minutes for 1-square-kilometer areas to determine the timing of evacuation. Nearly all local governments also have a hotline that enables the heads of meteorological observatories nationwide to call the heads of municipalities directly to warn them of an imminent disaster.
Efforts are also being made in local communities. In the Mabi district of Kurashiki, Okayama Prefecture, about one-third of which was flooded by the torrential rains in western Japan, residents are working on a system called "My Timeline" to plan out their own actions before disasters strike.
"Improving infrastructure is an effective measure against flood disasters, but it's impossible to prevent river flooding during all heavy rains," said Koji Ikeuchi, a professor at the University of Tokyo who specializes in river engineering. "On the assumption that floods will occur, it is necessary for residents themselves to understand information including the likelihood of floods in advance, and learn to evacuate appropriately," he added.
Read more from The Japan News at https://japannews.yomiuri.co.jp/
