Inflow into Korea's Soyang Dam: Hydrologic variability and links to typhoon impacts

East Asia, including the Korean Peninsula, is exposed to the typhoon-related risk, especially in the form of flooding. The aim of this study was to determine the hydrologic variability characteristics of the Soyang River Dam—a representative multipurpose dam in the Korean Han River basin—with a particular focus on the quantitative assessment of the sensitivity of daily inflow into the dam basin and the related typhoon-impacts. Although the frequency of typhoons occurring in the western North Pacific Ocean region does not indicate any distinct increases, typhoons passing the domain of the Korean Peninsula change the summer flow of the Soyang River Dam significantly. Analysis results suggest that 22.6% of the summer flow in the Soyang River Dam can be attributed to typhoons. Furthermore, during the periods characterized by the transition from El Niño to La Niña, typhoons exert a large influence on the hydrologic regime. The frequency of typhoon occurrence is highly correlated to the typhoon-induced flow, and the occurrence date of peak flows when typhoons strike was determined to be significantly delayed compared to that of the average years (1974–2015). In addition, low-flow metrics show downward trends, however, there is no distinct correlation with the statistical data of typhoons. The results from this study offer baseline information for mid- and long-term plans that cope with natural disasters or the supply of water resources for humans and natural systems according to the seasonal flow patterns of basins. The links to typhoons signify the critical importance of integrative analyses that consider hydrologic and meteorological phenomena.