An Integrated QGIS-Based Evacuation Route Optimization Approach for Disaster Preparedness Against Urban Flood in Japan

Urban inland flooding has become a serious problem in many cities because heavy rain often exceeds the capacity of drainage systems. In Japan, GIS-based evacuation maps are commonly used to support disaster preparedness, but they still have several limitations. In particular, they do not avoid flooded road segments and cannot generate multiple evacuation options at the same time. This study proposes an improved evacuation route method using the free and open-source software QGIS. The method combines flood-depth data with road network processing to remove roads where the predicted water depth is higher than 0.5 m. It also provides several evacuation paths to different shelters at the same time. A case study in Kurashiki City, Okayama Prefecture, demonstrates that about 1.37% of the road network becomes unusable during an inland-flood scenario. Several existing evacuation routes also pass through hazardous areas, but the QGIS-based method avoids these areas in most cases. Since the workflow uses only built-in QGIS functions and does not require programming or plug-ins, it is easy to reproduce and apply in other regions. This study offers a practical and low-cost method to support inland-flood evacuation planning for local governments.