Cost Benefit Analysis of Several Adaptation Measures through Flood Inundation Simulations based on Climate Change Impacts in Rivers of Toyama Prefecture, Japan

Abstract Submission: Frequency and magnitude of the flood inundation disasters are increasing due to climate change in Japan, and several adaptation and counter measures should be implemented in the river basins. This study presents a cost-benefit analysis of flood damage and various adaptation measures for the Oyabe, Jinzu, Sho, Joganji and Kurobe Rivers in Toyama Prefecture, Japan. The rainfall runoff and flood inundation simulations considering the climate change impacts were conducted at the target rivers. For the climate change analysis, d4PDF (database for Policy Decision making for Future climate change) were utilized in this study. The d4PDF data provide detailed 5 km mesh for future climate data with large ensemble members. This large ensemble member makes us compute the flood return periods of the target events and evaluate the uncertainty of the simulations. Several counter measures such as paddy field dams and vegetation management in the rivers were evaluated on this study because of the green infrastructure aspects and mitigation effects of the climate change.
The evaluation results showed that paddy field dams were effective in the target rivers, especially in the Oyabe River, where the cost-benefit was 12.6 at 50% implementation rate and 14.9 at 100% implementation rate. Also, it was confirmed that the vegetation management in the rivers are useful as the counter measures from cost-benefit analysis. In addition to the cost-benefit analysis, we evaluated the effects of the counter measures on the flood inundation risk based on the levee erosion potential. The results of the analysis show that the probability of inundation in the inner area of the levee, the probability of inundation above floor level, and the probability that horizontal evacuation was reduced by the counter measures.

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