River-Basin Classification for Flood Risk Assessment in Indonesia

The risk of water-related disasters is increasing globally due to climate change, but varies depending on land use, population, and watersheds. This study presents a classification method for flood risk assessment that allows appropriate mitigation measures to be taken based on regional characteristics. A case study was conducted in Indonesia, which has unique geographical characteristics, such as the Asian Monsoon Zone and high rainfall. First, a database on the topography, climate, and population demographics of each river basin will be maintained in the GIS by using an open-source dataset. We extract areas that may be inundated by some types of floods by applying simple assumptions to topographic dataset such as Digital Elevation Maps (DEM), Grid Point Values (GPV), and Height Above Nearest Drainage (HAND). The results of aggregating the population exposed to hazardous areas by subdistrict showed a very large range in the exposure ratio, from 0.0 to 0.88. The analysis, which also considered the poor ratio of each subdistrict, revealed a ranking of the poor population exposed to flooding. These results suggest useful information for proposing effective mitigation tailored to local characteristics. These results demonstrate the advantages of focusing on the characteristics of the exposed society in water-related risk assessment. It is hoped that the classification can guide readers in determining targeted disaster prevention and mitigation policies.