Resilient Economies Strategies for Sinking Cities and Flood Risks 2025

Groundwater regulation governance in Tokyo FIGURE 5 Ministry of Environment Regulates basic environmental law, industrial water law and building law4Ministry of Economy, Trade and Industry Sets policy on industrial water use and guidelines3 Ministry of Agriculture, Forestry and Fisheries Sets policies on agriculture-related resources, measures for subsidence, and observes irrigation water using groundwater2Ministry of Land, Infrastructure and Tourism (MLIT) – River Bureau Regulates on river water maintenance, uses and preservation5 Ministry of Land, Infrastructure and Tourism (MLIT) – Water Resource Bureau Manages the basics plan for water resource, and provides guideline for prevention of ground subsidence6Ministry of Health, Labour and Welfare Sets policy on water supply and quality1 Bureau of Environment Operational arm for groundwater management under TMG, enforcing local regulation8 Tokyo Metropolitan Government (TMG) Builds regulation and technical guideline upon national laws7Central government office Cross-sector and national-level enforcement and oversight body for national government laws Source: Hori, S. (2016). The Structure of Local Groundwater Law for Sustainable Groundwater Policy in Japan. Laws, vol. 5, no. 19. https://doi.org/10.3390/laws5020019. –Water infrastructure: Tokyo shifted from groundwater reliance to surface water resources, expanding water treatment plants and distribution networks. Today, some 600 facilities with water purification plants, supply, distribution and pump stations, and source wells provide water.99 Coupled with demand- side efficiency and leakage reduction, this alleviates pressure on aquifers, addressing a root cause of sinking. Additionally, investments in drainage systems such as the Metropolitan Area Outer Underground Discharge Channel have prevented over JPY 150 billion in potential flood damages since 2006.100 Its effectiveness was demonstrated during Typhoon Hagibis in 2019, diverting over 12 million cubic metres (m3) of floodwater.101 While the system does not directly prevent subsidence, it reduces erosion and other risks. –Nature-based infrastructure: Since 2001, local ordinances have required green roofs, vertical gardens or vegetation on 20–25% of new and renovated building areas between 1,000 and 5,000 square metres (m²). As of 2024, over 5,700 new or existing buildings feature 180 hectares of rooftop greenery.102 Conservation of green areas, rainwater infiltration and reclaimed wastewater initiatives further support groundwater recharge and flood mitigation.103,104 –Technology and data: Authorities support subsidence and flood management using data from traditional and advanced technologies, in engagement with agencies like the Geographical Survey Institute (GSI) and the Japan Aerospace Exploration Agency (JAXA). Observation wells and surveys, global navigation satellite systems and interferometric synthetic aperture radar (InSAR) provide data to track land subsidence and inform infrastructure planning. Resilient Economies: Strategies for Sinking Cities and Flood Risks 19