KAZUNARI HANAWA, Nikkei climate change editor, and WATARU SUZUKI, Nikkei staff writer
This Nikkei Asia Big Story will also be published as part of a series on climate change led by Taiwan’s CommonWealth magazine, in recognition of the United Nations’ World Environment Day, which fell on June 5.
TOKYO — In October 2019, Typhoon Hagibis made landfall on the Japanese coast near Tokyo, with winds of over 195 kph and waves as high as three-story buildings. The largest typhoon to hit Japan since records began, it slashed through towns and inundated low-lying coastal areas.
Facing the prospect of massive floods, authorities were able to fall back on a recently created defense mechanism: a system of artificial caverns dug into the rock and clay underneath Saitama Prefecture, north of Tokyo. By gulping down 12.18 million cu. meters of water — about 4,800 Olympic swimming pools worth — it saved Greater Tokyo from an estimated 26.4 billion yen ($201 million) of damage.
The underground channel, known as the Metropolitan Outer Area Underground Discharge Channel, runs for 6.3 km from east to west. Fifty meters below ground, 177 meters long and 78 meters wide, the pressure-adjusting water tank is a subterranean forest of 18-meter high cement columns that dwarf visitors and create an eerie, cathedral-like ambience straight out of a science fiction film.
Dubbed “The Underground Shrine” for its resemblance to a Greek ruin, the huge cavern was completed in 2002, just as Japan began to grapple with the extreme weather patterns of global climate change.
An island nation, Japan has lived with the risk of floods for centuries, but recently the rushing waters have become more frequent and destructive. According to Japan’s Ministry of Land, Infrastructure, Transport and Tourism, which is in charge of flood control, about 60 million people, or half of Japan’s population, live on the 10% of land that would sink below river level in the event of a flood. About 75% of Japan’s assets are also concentrated in these areas. Osaka and Tokyo, which accommodate large populations, have no choice but to locate near river mouths due to the country’s large number of mountains and lack of plains.
The effects of global warming — such as damage from heavy rainfall, larger typhoons and rising sea levels — are becoming increasingly evident in Japan and the world over. The incidence of short-duration heavy rainfall — storms that drop more than 50 millimeters of water in an hour — in Japan has increased by 40% in the past 30 years. The number of days with rainfall of 100 mm and heavy rainfall of 200 mm or more has also increased.
It is no longer unusual for floods to occur, costing property and lives. Floods also spawn further disasters: The annual average number of landslides in Japan from 1990 to 2009 was about 1,000 per year. Since 2010, the average has been 1,500 a year.
Torrential rains cause severe damage every year, and flood control measures have not kept pace. “Recently, there have been a lot of torrential downpours,” said Nobuyuki Akiyama, chief of the Metropolitan Outer Floodway Management Office. “Small rivers are now overflowing quickly.”
Japan, however, is tackling this and other of Mother Nature’s tantrums by applying its technological chops: from swaying earthquake-proof buildings to a satellite-based early warning system for volcano eruptions and tsunamis.
The highlight of the flood management facility is a colonnaded pressure regulating tank that temporarily stores water in the event of flooding. Connected to the tank is a 70-meter-deep shaft. The water is taken into a cylindrical space that could easily fit a space shuttle.
The massive underground flood channel is perhaps the most impressive but far from the only technological marvel that Japanese authorities have deployed to reduce potential flood risk.
Kansai International Airport: A floating target
Located on an artificial island near Osaka, off the southwest coast of Japan’s main Honshu Island, Kansai International Airport is the country’s third-busiest air terminal. Compared to Narita International Airport, not too far from Tokyo, it is far more vulnerable to water damage.
When a magnitude-9.0 earthquake triggered a tsunami on Japan’s northeast coast in March 2011, the Fukushima Daiichi nuclear plant suffered power outages due to severe flood damage to underground power sources.
The airport was left similarly powerless in September 2018, when Typhoon Jebi hit, knocking out the facility’s underground power station and stranding around 8,000 passengers. Both disasters made headlines around the world.
“The airport was opened in 1994, so the issue of a disaster like Fukushima was not taken into account,” said Yoneda Yutaka, leader of a crisis management group at Kansai airports. “Now we have moved [the power sources] to a higher location to prevent flooding.”
After Typhoon Jebi, the airport launched a mega engineering project: a 6-km section of the island that holds the airport has been raised by around 2.7 meters. Wave-extinguishing blocks were added to approximately 4.5 kilometers of the east and south sea walls, which were subject to significant wave battering.
The project, which cost 54.1 billion yen ($408 million), is expected to reduce the estimated amount of inundation to one-270th of that caused by the typhoon in 2018. The height of the waves is being addressed based on a projection of sea-level rise made by the Intergovernmental Panel on Climate Change (IPCC) and other factors.
If a large typhoon is expected, the airport will halt takeoffs and landings in advance to prevent passengers from being stranded. Other precautions will also be taken. Kansai International Airport will be the gateway to Expo 2025 Osaka, which is expected to showcase exhibitions from 100 countries and regions and bring in 28 million visitors.
“We will consult with surrounding municipalities and other organizations to create an evacuation plan and prepare for the unexpected in terms of both hardware and software,” Yoneda said.
Protecting Japan’s trains
In 2015, Japan’s government summarized a climate change adaptation plan based on a report by the IPCC and discussions at the Conference of the Parties (COP) 21 in Paris.
In addition to building dams and strengthening levees, the government decided to address flood damage from both hard and soft aspects, such as establishing evacuation plans in cooperation with local governments and encouraging people to relocate their homes in consideration of disaster risks.
While the “Underground Shrine” under Saitama mitigated the damage in Tokyo, Typhoon Hagibis told policymakers there was an urgent need for a new response. This is because 120 cars of Japan’s world-class Shinkansen bullet trains were submerged and scrapped after the Chikuma River burst its banks in Nagano. The total loss was estimated at about 14.8 billion yen ($111 million). The electrical systems that control the motors and other equipment under the floors were damaged.
“Considering safety and stability, we decided that it would be more appropriate to build new trains rather than repair them,” Yuji Fukasawa, president and CEO of East Japan Railway, told reporters.
Shinkansen trains, a key means of transportation in Japan, are vulnerable to flooding. The railcar yard in Nagano Prefecture was located in a flood-prone area that a hazard map said could be inundated by 10 or more meters of water. The 2 meters of fill that was placed to prevent flooding was inadequate.
About 60% of all Shinkansen rail yards in Japan are located in flood-prone areas. Trainyards require a large flat area, and in mountainous Japan, relocating to higher ground is not an easy task. There is also a limit to how much land can be raised or filled in. For this reason, Japan’s railway companies have established evacuation plans for railcars, and when a large typhoon or heavy rainstorm is forecast, they evacuate railcars to stations on higher ground.
The accuracy of rainfall forecasts is also important. However, as climate change rages on, the Japan Meteorological Agency has not been able to adequately forecast the damage caused by heavy rainfall. “We were not good enough,” Yasuo Sekita, then-director-general of the Japan Meteorological Agency, said in response to the string of disasters. “We will improve the accuracy of our forecasts.”
Researchers from Imperial College London and the University of Oxford have estimated that the amount of damage caused by Typhoon Hagibis was about $10 billion, of which about $4 billion was caused by climate change effects such as rising sea temperatures.
Japanese Emperor Naruhito has also expressed the importance of tackling climate change. “A wide range of stakeholders must work hand in hand to achieve a decarbonized society,” he said during a news conference marking his 62nd birthday in February.
Tokyo, like many Asian cities, is extremely vulnerable to water damage. Tokyo Metro, which operates the capital’s main subway system, is taking measures based on a flooding simulation by the Central Disaster Management Council that also takes into account the effects of climate change.
Tokyo Metro operates a 195-km network across the metropolis. Typhoon No. 22 in 2004 actually submerged part of a station.
A Ginza Line train yard squats in a neighborhood of Tokyo’s Ueno district that is otherwise filled with buildings. The area is surrounded by large rivers such as the Arakawa and Sumida, and is often referred to as a “zero-meter zone” that is at risk of flooding.
In September 2021, Tokyo Metro began preparing for flooding of the Arakawa River. A waterproof gate capable of withstanding the pressure of water up to 6 meters deep was installed between the tracks and the aboveground detention area directly connected to Ueno Station. The gate can be lowered in less than two minutes to prevent water from entering.
“Until now, we have been vulnerable to flood damage from the Arakawa River,” said Shunya Noguchi, deputy manager of the subway operator’s safety affairs department. “We have taken measures based on national flooding forecasts.”
When there is a forecast for a large typhoon, planned service suspensions will be implemented to prevent passengers from being stranded underground due to flood damage.
Even so, Toshiaki Kogure, deputy director of Tokyo Metro’s safety affairs department, points out that “it is sometimes difficult to predict sudden torrential downpours, such as those caused by linear precipitation zones.”
Railroad and airport operators are responsible for the lives of their passengers. Therefore, response measures are taken seriously.
The economic cost of climate change
It is not just infrastructure that is at risk. Climate change also poses a challenge to Japan’s public administration. The low economic growth that has continued since the 1990s, the declining birthrate and aging population have depleted financial resources that might otherwise be available for dam construction, levee reinforcement and other large-scale public works projects.
In the aftermath of torrential rains that hit Kumamoto Prefecture in July 2020, plans emerged to build a dam upstream on the Kuma River. The project did not go ahead due to concerns about the impact on the ecosystem and criticism that the huge cost would be wasteful.
In 2008, Kumamoto Gov. Ikuo Kabashima had demanded a blanket withdrawal of the dam project. In 2009, with the Democratic Party of Japan in power nationally, he announced that construction had been suspended. The DPJ administration was critical of large-scale public works projects and promoted what it called a “from concrete to people” policy in which budgetary outlays were to be shifted from public works to welfare programs.
Eleven years on, however, Kumamoto was inflicted with damage that cost lives, causing Gov. Kabashima to approve the construction of dams. “Global warming,” he said, “has changed the way rain falls.”
But the cost of another round of flood control projects across Japan remains prohibitive. Kumamoto’s flood hazard has highlighted a challenge: How can Japan balance its national finances?
National and local governments are combining hard and soft measures. The soft measures include land-use restrictions and urban development in line with hazard maps. Government officials are beginning to explore the importance of flood control, including the beefing up of evacuation systems.
In eastern Japan, which took the brunt of Typhoon Hagibis, the government and local residents have been working together to mitigate flood damage by intentionally flooding rice paddies and turning them into reservoirs.
“In the past, people thought it was outrageous to flood precious rice paddies,” a senior Environment Ministry official said. But this perception is gradually changing in the face of rapid climate change.