Deep below the streets of Tokyo, a colossal tunneling machine has ground a path through the earth.

Over 13 meters (42 feet) wide, the shield tunneling machine lays concrete walls as it goes, leaving behind a 4.5 kilometer (2.8 mile) tunnel designed to capture vast quantities of rain that might otherwise flood the homes above.

Tokyo already boasts an extensive system of tunnels, drainage channels and storage cisterns, but like much of the world, Japan is coping with unprecedented weather due to climate change, forcing it to dig once more.

The summer of 2024 was the hottest since records began in 1898, Japan's weather agency said in September. In Tokyo, sudden, violent storms known as "guerrilla" downpours have become increasingly commonplace.

"We believe that by 2050 as the global temperature rises by 2 degrees Celsius, rainfall amounts will also rise by 1.1 times," said Shun Otomo, a construction site manager for the Japanese capital's construction bureau.

"As the climate changes, these kinds of rains are expected to become more and more frequent and to have even greater impact, so we intend to strengthen the provision of these facilities in order to ensure the safety and security of the people of Tokyo," he said.

Just after 5 a.m. on August 30, Tokyo's flood defenses went into action as water began flooding into a cavernous chamber known as the "underground cathedral" north of Tokyo. The gushing water, captured by subterranean security cameras, was rain pouring into the capital region as Typhoon Shanshan lashed southwest Japan, 600 kilometers (372 miles) away.

The cavernous expanse has enough volume to fit almost 100 Olympic-size swimming pools of water.

Inside are 59 massive pillars, each weighing 500 tonnes and stretching 18 meters (59 feet) to the ceiling. When nearby rivers flood, the overflow courses through 6.3 kilometers (3.9 miles) of massive underground tunnels before collecting in the underground cathedral — officially known as the Metropolitan Outer Area Underground Discharge Channel.

Yoshio Miyazaki, the land ministry official in charge of the cathedral, estimates that over 150 billion yen ($1.03 billion) in damage has been mitigated since the complex was built 23 years ago.

The system kicked in four times in June, more than all of last year. During Typhoon Shanshan, it captured enough water to fill the Tokyo Dome baseball stadium almost four times, before pumping it safely into the Edogawa River and out to sea.

As the climate continues to warm due to the effect of man-made emissions, Tokyo's rainfall looks set to lay an even heavier burden on the city's flood defenses, said University of Tokyo professor Seita Emori.

"The basic cause is that as the temperature rises, the amount of water vapor in the atmosphere increases, meaning that relatively larger quantities of rainfall," Emori, a co-author of a Nobel Prize-winning Intergovernmental Panel on Climate Change (IPCC) climate report, said.

"We are now in a long-term warming trend, so we anticipate that previously unseen record amounts of rain will fall as the temperature rises in future," he said.

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(Production: Tom Bateman)