Hydrological extremes in megacities - the Tokyo case

Tokyo Metropolitan University (TMU), operated by Tokyo Metropolitan Government (TMG), has improvement of the urban environment in mega-cities as its priority issue. Part of this is improving assessment of future changes in flood risks in Tokyo, an important issue for climate change adaptation. Analyses of design rainfall changes, urban storm runoff and inundation scenario simulations will be made with tailored indicators to help improve flood risk assessments.


Issue to be addressed

Design rainfall is used when designing sewer systems and other components of the urban water management system. Design rainfall used for the planning of small and medium rivers has recently been evaluated by the historical data in the Bureau of Construction, TMG. To adapt to future climate change, impact assessment of probable changes in extreme rainfall based on future projections is needed.

Decision support to client

The client is aware of changes in design rainfall change, as compared to the present design rainfall, and its impact to small and medium rivers under climate change conditions. The key issue is how to take climate change impacts into account in guidelines and recommendations. Decisions on modificatons of design storm characteristics can have a very large impact for practitioners.

Temporal and spatial scale

Adaptation measures will be implemented from 2 to 100 years in the future, for all of Tokyo. The spatial scale for urban storm runoff and inundation analysis is about 10km2.

Knowledge brokering

TMU was is founded by TMG and there is an agreement between Department of Civil and Environmental Engineering (part of TMU) and Civil Engineering Support and Training Center under Bureau of Construction (part of TMG) for research partnership on problems related to social infrastructure. Monthly meetings will be held to report progress, discuss results and remaining work. It is possible to use this case study to build cooperative research between the two departments in the near future.


Poster displayed at the Kick–Off meeting, 7/8 September 2017, Norrköping, Sweden

Distribution of times for hourly rainfall of 50 mm