Estimating Land Use Changes due to Levee Improvement: A Case Study of the Kiso River Basin in Japan from the 1890s to 2000s

The development of modern flood control infrastructures has reduced the human and economic damage caused by floods. Nevertheless, the reduced frequency of floods may increase the number of people in the floodplain because of low awareness of disasters, thus increasing the exposure of society (Di Baldassarre et al., 2013). To examine this human-water interaction, in this study, we empirically analyzed how flood control infrastructures (i.e., levees) have affected land use in the floodplain. We considered the Kiso River basin in Japan as the research domain, where the population has significantly increased over 100 years. The traditional flood control culture that involves living with discontinuous levees known as "Kasumi levees" and "Wajyu levees" (ring levees) has rapidly replaced modern flood control technologies. We attempted to understand the impact of levee improvement when dealing with various complex factors that influence land use. Land use in hazardous areas can be affected not only by levees but also other infrastructures and industries that are located in the area; this can bias the estimation of the impact on land use "with" and "without" levees. We employed the propensity score method (PSM) to control these variables that influence the impact estimation. PSM is a quasi-experimental method that generates an artificial control group (area "without" levees) by matching each treated area (area "with" levees) with a non-treated area having similar characteristics. We also employed the difference-in-differences method for the time-series change detection of the data controlled by the PSM. We generated the data from maps of the Kiso River basin from the 1890s to the 2000s. These maps are provided by the Geospatial Information Authority of Japan. They are of uniform quality and depict the entire land area of Japan. We traced not only levees and land use but also the location of schools, industries, and infrastructures in the Kiso River basin as GIS data and developed them as panel data. Finally, we identified the affected area by installing modern flood control facilities such as levees and when the impact emerged.