Comparing a Single-Hazard Map and a Multi-Risk Overlay Map Based on Design with Nature Process

The magnitude 9.0 earthquake and tsunami that struck Japan’s Tohoku region in 2011 highlighted the critical need to integrate disaster risk prediction into post-disaster reconstruction. Building on this perspective, this study evaluates the predictive accuracy and practical utility of two risk assessment methods—the Ministry of Land, Infrastructure, Transport and Tourism hazard map, which is based on single-hazard, uniform physical criteria (single-hazard map), and a multi-hazard overlay map based on McHarg’s ecological planning approach—in the context of the 2024 Noto Peninsula Earthquake and subsequent rainfall-induced sediment disasters in Wajima City. Using QGIS-based spatial analysis, we quantified and compared the spatial overlap between pre-disaster risk predictions and actual sediment-disaster damage. We also examined the relationship between potential housing relocation sites identified through interviews and the two risk maps. The results show that the single-hazard map explained only 16% of the damaged areas in Wajima City and 9% in the Najimi District, whereas the multi-hazard overlay map accounted for all affected zones and clarified the underlying environmental factors. Moreover, the official single-hazard map showed minimal spatial overlap with proposed post-disaster relocation sites. In contrast, the overlay map not only visualized complex multi-hazard risks but also provided insight into differences in disaster risk among potential residential relocation sites and their underlying causes. These findings suggest that reliance on single-hazard maps may result in substantial blind spots in both disaster preparedness and post-disaster recovery. By contrast, overlay-based composite mapping demonstrates both quantitative and qualitative potential for comprehensive regional evaluation and visualization in risk assessment and reconstruction planning.