Assessing Multidimensional Future Flood Risk across South Korea Using an Integrated Flood Risk Index Based on IPCC AR6 Scenarios

Climate change has led to increasingly complex alterations in flood characteristics across South Korea, with changes in flood frequency, magnitude, and duration occurring in different and sometimes opposing directions. This evolution has resulted in the expansion of multidimensional flood risk, which cannot be adequately captured by conventional flood assessments focusing solely on peak discharge. In particular, the increasing occurrence of extreme rainfall events and localized torrential storms highlights the need for a new assessment framework that integrates multiple flood characteristics to better anticipate future flood risks.

In this study, an Integrated Flood Risk Index (IFRI) was developed using IPCC AR6-based future climate scenarios and nationwide runoff simulations to comprehensively assess future flood risk across South Korea. Daily runoff was simulated from 1981 to 2100 using the Soil and Water Assessment Tool (SWAT), with 774 sub-basins across the five major river basins adopted as spatial analysis units. Among 20 climate change scenarios provided by the Korea Meteorological Administration, seven representative RCM–SSP combinations were selected based on a climate variability and extremity screening method proposed by Kim et al. (2025). Analyses were conducted for a historical reference period (1991–2020) and two future periods: mid-century (2031–2060) and late-century (2061–2090).

The IFRI was constructed by integrating information on both flood frequency and intensity derived from runoff simulations. As a core component, the Standardized Flood Index (SFI) was calculated by standardizing short-term accumulated runoff using a log-normal distribution, with flood events defined when SFI values exceeded +1.0 or corresponding high-percentile thresholds. Based on the IFRI, future flood regime changes were quantitatively classified into four distinct types (Type 1–4), representing different patterns of flood risk evolution.

The results reveal pronounced spatial variability in future flood risk across South Korea, with a marked intensification of flood hazards in many regions during the mid-century period, followed by partial moderation in the late century while maintaining elevated risk levels. The shortening of flood return periods indicates an increased likelihood of more frequent and severe flood events. These findings provide a robust scientific basis for national-scale flood risk assessment and emphasize the need to strengthen climate-adaptive flood management and planning strategies.