Effectiveness of Investing in Flood Protection in Metropolitan Areas: Lessons From 2019 Typhoon Hagibis in Japan

Climate change is increasing the severity, frequency, and duration of flood risks and events. Therefore, investment in flood protection measures is crucial to protecting lives in increasingly populous areas. This paper aims to demonstrate the effectiveness of investment in flood protection measures in Tokyo by analyzing the severity of flood damage caused by Typhoon Hagibis, which unleashed record-breaking rainfall on Japan in October 2019.

The paper examines flood risks in the Greater Tokyo Area and reviews how flood protection systems have functioned to prevent and minimize flood damage. The analysis utilizes hydrological data of rainfall, water levels of major rivers, and operation records from flood control facilities. The paper has practical implications for all countries and cities facing flood risks due to climate change. Indeed, this paper provides detailed descriptions of flood protection systems, including upstream dams, midstream reservoirs, and downstream diversion channels.

This paper was written as part of the research project titled “Research on Demand Estimate on Infrastructure in Asia” conducted by the JICA Ogata Sadako Research Institute for Peace and Development.