Year after year, cherry blossoms in Japan announce the end of winter and usher in the season of pink. But there was something special, and alarming, about the blooming cherry trees this year.
In what scientists said was likely a symptom of climate change, Kyoto’s cherry blossoms peaked on March 26, the earliest since official records began in 1953. Between then and 2020, average March temperature in Kyoto rose from 8.6 degrees Celsius to 10.6 C.
Early cherry blossoms seem harmless enough. But climate change also exacerbates extreme weather events, such as intense rain and floods.
To combat flooding, Japan has created gargantuan underground flood diversion systems.
The Metropolitan Area Outer Floodway, located on the outskirts of the Greater Tokyo Area, is one of the world’s largest underground drainage tunnels.
The “underground temple” diverts floodwater to protect the 38 million residents in the Tokyo metropolitan region.
“Intense heavy rains, disasters that may have occurred once every 100 years, are becoming more regular because of global warming. They’re now occurring once every 50 years, or once every 30 years,” said Kei Yoshimura, a professor at the University of Tokyo specializing in hydrology.
“Tokyo’s floodway systems help prevent most disasters,” Yoshimura told VICE World News.
Takeshi Ōyama, a spokesperson for the Edogawa River Office, which manages the floodway, said the system has been effective especially for the Saitama region, which is part of the Greater Tokyo Area and is historically vulnerable to floods caused by typhoons and torrential rain.
Since its partial completion in 2002 to 2019, the system has been used 121 times to store excess floodwater.
In July 2000, a devastating typhoon brought heavy rain that flooded 248 homes in the Saitama region. After the system’s full completion in 2006, however, fewer homes have been damaged during typhoons.
In December 2006, a storm with even greater rainfall than the 2000 typhoon flooded only 85 homes, according to the Edogawa River Office.
The colossal underground space holds five 70-meter deep wells big enough to hold the Statue of Liberty. These wells are connected through a maze of underground tunnels supported by pillars each weighing 500 tons.
Construction on the floodway began in March 1993, in an effort to prevent flood damage in the Greater Tokyo area. The land surrounding this system is shaped like a bowl, and therefore accumulates rainwater and floods easily.
Increased use of asphalt to urbanize Tokyo has also made it harder for the ground to absorb rainwater. During heavy rainfalls, nearby small- and medium-sized rivers would flood easily and overwhelm drainage systems.
During the dry season, typically August to May in Tokyo, the floodway is open to visitors. Harness and helmet are required at parts of the tour.