Cost-benefit analysis of adaptation measures to reduce flood inundation damage in rivers in Toyama Prefecture, Japan

In recent years, the scale and frequency of torrential rains and floods have increased globally due to climate change. Under this situation, Japan’s flood control policy was shifted to the basin-wide flood control named “River basin disaster resilience and sustainability by all,” and many counter and adaptation measures have been proposed to be implemented in several basins. This study presents a cost-benefit analysis of various adaptation measures for reducing flood damage in the Oyabe, Jinzu, Joganji, and Shogawa Rivers in Toyama Prefecture, utilizing a flood inundation model with future climate data (d4PDF). This study focuses on paddy field dams (PFDs) and river vegetation cutting and removal (VCR) because of their green infrastructure benefits and climate change mitigation effects. PFDs were effective in the Oyabe River, where the cost-benefit ratio reached 2.98 at a 50% implementation rate and 3.48 when fully implemented in the target area. Additionally, the VCR in rivers proved to be a useful countermeasure based on the cost-benefit analysis, especially for Shogawa River. However, the overall cost of VCR should be minimized by prioritizing specific areas within rivers.