Impact of Rainfall Control on Socio-economic Flood Risk Assessment in the Kurokawa River Basin, Japan

Flood inundation damage to the socioeconomic landscape caused by short-term extreme rainfall has been a primary concern for years, particularly regarding shifts in precipitation patterns driven by climate change. To mitigate these impacts, many studies have prioritized the enhancement of flood prevention infrastructure in high-risk areas. However, the construction of permanent facilities requires rigorous scientific assessment and significant investments of time and capital. As an alternative to traditional infrastructure, weather modification strategies are being explored to reduce societal impacts. These strategies include suppressing the formation of cloud systems by altering air currents through the construction of physical obstacles, as well as removing water vapor via proactive cloud seeding. To evaluate the efficacy of seeding in reducing flood risk, we utilized simulated rainfall data from the Weather Research and Forecasting (WRF) model, which incorporates a seeding core module to test rainfall control effectiveness within the Kurokawa River basin, Kyushu, Japan. The results demonstrate that a 10% reduction in 24-hour basin-averaged rainfall led to a 20% decrease in peak discharge (excluding overflow). Correspondingly, the inundation extent was reduced by 20% across different scenarios, with the most significant improvements observed in high-depth areas. To quantify the benefits for stakeholders and the government, this study evaluated potential economic losses. The reduction in inundation successfully mitigated agricultural and property economy losses by approximately 10%. Furthermore, we assessed threats to human life by proposing critical water depth thresholds specific to elderly populations (aged over 65 years old) and younger residents based on housing types and government data. These metrics confirm that rainfall control strategies effectively safeguard the community and the broader economy against climate-driven flood disasters.