Abstract
Abstract Against increasing number of unprecedented heavy rains and typhoons reflecting climate change, the Japanese Government decided saving life as the top priority considering a ‘worst-case’ scenario. Accordingly, the Flood Risk Management Act was amended in 2015 to use the anticipated maximum scale precipitation (AMSP) for flood inundation calculation. In order to estimate the AMSP, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) chose historical maximum areal precipitation in the form of duration–area–depth (DAD) curves rather than climate change projections' dataset d4PDF. In this paper, policy development and detailed estimation procedures for the AMSP were reviewed and discussed. It was concluded that the current climate change projections are still not accurate enough to be used as the basis for real local operations, while long accumulated ground observations and ground-based radars are available in good quality all over Japan. But at the same time, historical maximum should always be updated as past records are renewed. Also, regional partitioning should not be done at too coarse of scale for proper regionalization of DAD. Such strategy would serve as a useful reference for other nations.
Highlights
Methodology for estimating the anticipated maximum scale precipitation (AMSP) Regional partitioning for regionalization unit The method of identifying the AMSP was specified by the guideline (MLIT, 2015b) that uses the DAD estimated by the largest ever observed areal precipitation in the past that is available in the network of observation stations of Japan Meteorological Agency (JMA), instead of extreme values that are derived from rainfall projections under a future greenhouse gas emission scenario
A series of developments in Japan for climate change adaptation were reviewed, namely, policy priority to save life anticipating the worst-case scenario, hazard maps based on the AMSP, use of observed precipitation data rather than climatological projections to estimate the AMSP, regionalization of DAD curves for the AMSP estimated by historical maximum areal precipitation, distribution of hyetographs in sub-basins selected from the past disaster cases, enlargement method for hyetograph adjustment, and discharge and inundation simulation for hazard maps
Under the potential for climate change rapidly increasing the magnitude and frequency of hydro-meteorological extremes, it is necessary to take immediate action to prepare for saving lives and avoiding catastrophic economic losses prior to developing proper physical infrastructure. For such a critical goal, it is quite reasonable to anticipate the worst-case scenarios for floods, landslides, debris flows, similar to earthquakes, tsunamis, volcanic eruptions, etc., so that people can prepare for such emergencies and evacuate early enough to protect their lives
Summary
Climate change influences in Japan have been appearing most significantly in the form of intensification of hydro-met hazards such as heavy rains and typhoons causing serious floods, landslides and debris flows every. Water Policy Vol 23 No S1, 129 year especially since around the turn of the century Responding to such serious hazards, the Japanese Government has been taking a new strategy to overcome the situation.
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