Atmospheric teleconnection-based conditional streamflow distributions for the Han River and its sub-watersheds in Korea

An improved understanding of hydroclimatic variability is central to efforts that seek to anticipate and adapt water resources management in a variable and changing climate. In Korea's Han River Basin, warm season (June-September) streamflow contributes nearly 74% of the annual water supply. In this study, a 40-year record of simulated daily unimpaired streamflow for the Han River Basin and its 24 sub-watersheds is analysed with a view to identify relationships with atmospheric teleconnection patterns. Tree-based classification methods identify East Atlantic-Western Russia (EA-WR) and East Atlantic (EA) as the two dominant atmospheric circulation patterns that influence seasonal streamflow variability in the Han River Basin. The classification method allows partitioning of predictor space into three sub-regions, wherein conditional streamflow statistics were computed based on the joint phases of EA-WR and EA teleconnection indices. On the basis of conditional hydrologic-teleconnection information, we estimated the 50-year return period high- and low-flow events (fitted to a lognormal distribution), thus allowing a simultaneous assessment of the joint effect of changes in the mean and variability of streamflow. Application of this approach for the 24 sub-watersheds clarified the spatial coherence of teleconnection-related impacts on streamflow. Despite the relatively modest sample size, the approach presented here illustrates the potential for identification of conditional streamflow information based on climatic precursors. This diagnostic study is a critical first step in developing seasonal streamflow estimates conditioned upon large-scale climatic state, particularly for multi-objective reservoir and watershed management.