Cecilia Tortajada recalls making her way down a long staircase and into of one of Japan’s engineering marvels, an enormous water tank that crowns Tokyo’s defences against flooding. When she finally reached the tank’s ground, she stood among the dozens of 500-tonne pillars supporting the ceiling. In the cavernous, shrine-like cistern, she felt humbled.

“You find yourself being a tiny part of this humongous system,” recalls Tortajada, a water management expert at Lee Kuan Yew School of Public Policy’s Institute of Water Policy, in Singapore. “You realise how well prepared Tokyo is.”

If Japan is a pilgrimage destination for disaster and risk-management experts like her, this is one of its main temples. The floodwater cathedral hidden 22 meters underground is part of the Metropolitan Area Outer Underground Discharge Channel (MAOUDC), a 6.3 km long system of tunnels and towering cylindrical chambers that protect North Tokyo from flooding.

In the past several decades, the Japanese capital perfected the art of coping with typhonic rains and moody rivers, and its intricate flood defence system is a global wonder. But the future seems uncertain as the climate changes and rain patterns shift.

Tokyo’s battle with flooding stretches back through its history. The city sits on a plain crossed by five rowdy river systems and dozens of individual rivers that naturally swell each season. Intense urbanisation, rapid industrialisation and imprudent water extraction that caused some regions to sink have exacerbated the city’s vulnerability.