In the summer of 1742, two typhoons swept across Japan in quick succession, bringing torrents of heavy rain and flooding major rivers. Records from a young monk who witnessed the floods describe a muddy wave destroying levees and sweeping through villages. As levees and rivers collapsed, floodwaters rose in Edo, Japan’s largest city and political capital, abating only days later, and resulting in fatalities of a reported 6,000 in the city.
While floods were not an uncommon occurrence in Japan, the Great Kanto Flood of 1742 was the worst flood in the country’s early modern era, and the first flood disaster in its largest urban area. It highlighted the river engineering changes that had facilitated the growth of Edo, but also increased the city’s vulnerability to floods.
Today, while the threat of flooding remains high for Edo’s successor, Tokyo, Japan’s capacity to manage urban flood risks has only strengthened. Japanese cities have developed and employed a dynamic suite of flood risk management measures, from regulations, plans, and strategies for basin-scale river improvement, advanced infrastructural solutions, to coordination and communication mechanisms.
The 2nd Technical Deep Dive (TDD) for Integrated Urban Flood Risk Management (IUFRM) explores Japan’s experience in mitigating flood risks, which offers valuable lessons for countries facing similar urban flood challenges. Supported by the Global Facility for Disaster Reduction and Recovery (GFDRR), the World Bank’s Urban Floods Community of Practice (UFCOP) promotes an integrated approach to urban flood risk management and aims to make knowledge on urban flood risk management accessible and applicable, and to facilitate the transfer of innovation, good practice and lessons.
Key lessons from Japan’s experience in integrated flood risk management include the following:
- Risk assessment and communication: Approaches must be selected based on flood type and local characteristics, reflect different stakeholders’ specific needs and objectives, and account for climate change uncertainty.
- Planning and prioritization: The national government plays an important role supporting local governments. City governments also have to broker consensus between stakeholders.
- Investment implementation: Wherever possible, measures should include multi-functional systems that provide other benefits in addition to managing flood risks. It is also necessary to design and implement clear governance mechanisms.
- Operations and Maintenance (O&M): Regular performance monitoring and evaluation of IUFRM measures; and regular inspection, maintenance, repair, and replacement work are required for sustainable O&M.
Organized in April 2016 and also hosted by Japan, the 1st TDD was structured around four themes: (1) the evolving approach in Japan; (2) planning to reduce flood risk; (3) integrating non-structural measures in flood risk management; (4) turning planning into investment in key structural measures.
This year’s edition builds on the lessons learned and feedback from the 1st TDD, focusing on the following issues: (1) urban flood risk assessment and communication processes; (2) the planning and prioritization of flood risk reduction investments; (3) the implementation of these investments; and (4) how these investments are operated and maintained with a view to sustainability. A series of Knowledge Notes complementing the TDD’s four topics will also soon be published.
Through its long history reflecting and learning from each urban flood disaster going back to the Great Kanto Flood of 1742, Japan has reevaluated its laws, plans, and measures. Japanese cities have over time improved their capacity to better cope with urban flood risks. The TDD and forthcoming Knowledge Notes provide a unique opportunity for collaborative learning from Japan’s experience, enabling countries to develop a deeper understanding of urban flood risks and the integrated approach required to manage risks effectively.
The 2nd TDD on IUFRM in Tokyo and Kobe from the 22nd to 26th April 2019, co-organized by UFCOP, the Tokyo Development Learning Center (TDLC), GFDRR, the World Bank Tokyo Disaster Risk Management (DRM) Hub and the Japanese Ministry of Land, Infrastructure, Transport, and Tourism (MLIT), and Kobe City, brings practitioners from around the world to learn from each other and international and Japanese experiences on IUFRM.
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