Scale-dependent flood hazard amplification under warming climates: a tropical cyclone Hinnamnor storyline in South Korea

Anthropogenic warming is expected to intensify tropical cyclone rainfall, yet how this intensification translates into flood peaks across complex river networks remains poorly understood. In this study, we employed a WRF-forced WRF-Hydro modeling framework using a Pseudo-Global Warming approach to quantify the propagation of intensified rainfall from tropical cyclone Hinnamnor in 2022 under historical (SST-1860), current, and future (SST-2050, SST-2090) sea surface temperature (SST) conditions. While basin-mean runoff increases by about 24–49% under warmer climates, peak flow response exhibits scale-dependent heterogeneity with a highly right-skewed distribution across reaches. Under SST-2050, the median peak flow increases are broadly comparable across all stream orders (approximately 51–53%). Under SST-2090, however, headwater streams (first and second order) show a median increase of approximately 72%, while downstream main-stem reaches (third and fourth order) remain below 50%, indicating that the scale-dependent amplification of flood peaks becomes more pronounced under stronger warming. These results suggest that while flood risk increases across the basin, the most significant departures from current conditions will be concentrated in small, rapidly responding headwater basins under late-century climate scenarios.