Resilient Economies Strategies for Sinking Cities and Flood Risks 2025

2.1 Tokyo’s comeback: the first sinking city to stabilize Population ~37 millionArea ~2,188km2 Context In Japan, Tokyo’s rapid rise as a global megacity during the 20th century brought significant environmental challenges, most notably severe land subsidence. Driven by unchecked groundwater extraction due to industrialization and growth, ground levels in some areas declined up to 24cm per year by 1968.90,91 The combination of land subsidence and extreme weather events, such as Typhoon Kathleen (1947) and Typhoon Kanogawa (1958), exposed Tokyo’s infrastructure gaps and led to increased flooding.92 Solutions Recognizing the existential risks, the national government and the Tokyo Metropolitan Government (TMG) implemented strategies over time that combined infrastructure investment, regulatory reform and ecological planning. Their approach reduced subsidence rates drastically over the years and positioned Tokyo as a model for urban resilience for subsidence (see Figure 5).93 –Regulatory innovation: Groundwater regulation was formulated at the national level, involving inter-ministerial coordination across areas such as water quality and supply, irrigation, river management, industrial water use and pollution control. Legislation such as the Industrial Water Law (1956) and Building Water Law (1962) imposed strict limits on groundwater use and well construction. It introduced reporting requirements and established penalties for non- compliance – e.g. up to JPY 100,000 (Japanese yen) in fines and imprisonmnt.94,95,96,97 The TMG subsequently developed technical regulations and operational guidelines, with implementation led by the Bureau of Environment. Government subsidies and the Multipurpose Dams Act (1957) enabled industry transitions and the development of dam infrastructure for water supply and flood control.98 Resilient Economies: Strategies for Sinking Cities and Flood Risks 18