Flood Risk Perception in an Inherently Flood-Prone Urban Area: Based on a Land Price Analysis in the Arakawa River Downstream Area, Tokyo

抄録

In urban developments, inherently flood-prone areas are often developed to pursue economic benefits within land constraints. This trend has been observed worldwide, particularly in fast-growing developing countries, but has also historically occurred in developed nations, resulting in concerns about the safe development paradox and underestimation of flood risk. If these circumstances are persistently entrenched and difficult to improve, urban development in inherently flood-prone areas could be an irreversible bottleneck to sustainable urban development. This paper examines flood risk perception in the Arakawa River downstream area in Tokyo by analyzing land prices from 2005 to 2024. Over these 20 years, the official flood hazard map was legally set at the design flood level in 2005 and enhanced to the probable maximum flood level in 2015. The analysis showed statistically significant land price decline effects due to both design flood risk and probable maximum flood risk, regardless of inundation rank. This result confirmed that flood risk has been well perceived by society and residents at least over the 20 years in the area. Further analysis suggested that even before 2015, land prices significantly reflected probable maximum flood risk, likely due to past experiences. However, the 2015 legal revision of the flood hazard map amplified land price decline effects in areas with high probable maximum flood risk (above 5.0 meters of inundation). The results indicate that hazard maps can serve as effective disaster risk information tools to support sustainable urban development.