Macroscale impact assessment of flood damage reduction from climate change adaptation policies

Abstract Adaptation policies are being increasingly implemented to cope with the increased frequency of natural disasters due to climate change. However, it is crucial to quantitatively evaluate the mitigating effects of these policies, as this allows for their assessment and prioritization. Therefore, this study sought to develop a nonlinear flood damage function for each administrative region of South Korea to quantify the potential damage caused by extreme rainfall events. Afterward, a power function was nested to model the coefficient of the flood damage function with regional factors characterizing each region's flood mitigation capacity. Here, regional factors were selected based on their linkage to two potential adaptation policies: enhancing retention reservoir and pumping capacity and enhancing river dike construction. The proposed evaluation framework was tested in 15 administrative districts in South Korea and the flood damage reduction effects of the two policy scenarios were estimated. The enhancement of retention reservoir and pumping capacity showed a 6.7% reduction effect, whereas enhancing river dike construction showed a 29.2% reduction effect. The implementation of both policies yielded a 34.3% reduction effect. Despite the limitations of this study, our findings still provide a quantitative comparison of the long‐term effects of national climate change adaptation measures. Additionally, accumulating more damage records would allow for the development of damage functions at a finer scale.