SUMMARYTo enhance local flood disaster mitigation, participatory approaches for community-based flood risk communication are proposed using the workshops based on a Plan-Do-Check-Action (PDCA) cycle. In our case study, risk communication for floods due to heavy rain and river flooding was implemented at the Kosen community in Kumamoto City, Japan, during 2006-2007. A community-based flood hazard and evacuation route map were produced during the workshops and verified through virtual desktop evacuation drills. The fundamental resident flood evacuation data was obtained through the evacuation drills and analyzed with respect to the timing of the announcement of evacuation information, walking speed during evacuation, and the locations of evacuation centers. Implementation of flood risk communication was found to be effective for the enhancement of residents' awareness of both self-and mutual-help efforts in community-based flood risk mitigation.

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This article proposes a new type of warranty policy that applies the "nudge" concept developed by Thaler and Sunstein to encourage homeowners in Japan to implement seismic retrofitting. Homeowner adaptation to natural disasters through loss reduction measures is known to be inadequate. To encourage proactive risk management, the "nudge" approach capitalizes on how choice architecture can influence human decision-making tendencies. For example, people tend to place more value on a warranty for consumer goods than on actuarial value. This article proposes a "warranty for seismic retrofitting" as a "nudge" policy that gives homeowners the incentive to adopt loss reduction measures. Under such a contract, the government guarantees all repair costs in the event of earthquake damage to the house if the homeowner implements seismic retrofitting. To estimate the degree to which a warranty will increase the perceived value of seismic retrofitting, we use field survey data from 1,200 homeowners. Our results show that a warranty increases the perceived value of seismic retrofitting by an average of 33%, and an approximate cost-benefit analysis indicates that such a warranty can be more economically efficient than an ex ante subsidy. Furthermore, we address the failure of the standard expected utility model to explain homeowners' decisions based on warranty evaluation, and explore the significant influence of ambiguity aversion on the efficacy of seismic retrofitting and nonanalytical factors such as feelings or trust.

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