Just after 5 a.m. on August 30, water began flooding a vast underground chamber called the "cathedral" just north of Tokyo. The gushing water, captured by security cameras, was the rain that was drenching the capital region as Typhoon Shanshan lashed southwest Japan, 600 km (373 miles) away.

Tokyo upgrades flood defenses with $250 million initiative to combat extreme storms and rainfall, expanding its underground reservoir system.