Influence of the El Nino/Southern Oscillation on South Korean streamflow variability

Deciphering the mechanisms through which the El Nino/Southern Oscillation (ENSO) affects hydrometeorological parameters in the tropics and extratropics is of great interest. We investigate climatic teleconnections between warm or cold phases of ENSO and streamflow patterns over South Korea using an empirical methodology designed to detect regions showing a strong and consistent hydroclimatic signal associated with ENSO. We calculate not only spatial coherence values by monthly streamflow composite formed over 2-year ENSO cycle and the first harmonic fit to detect candidate regions but also temporal consistency rates by aggregate composite and index time series to determine core regions. As a result, the core regions, namely, the Han river basin and the Nakdong river basin, are detected with a high level of response of ENSO phenomena to streamflow patterns. The ENSO composites for both core regions indicate drier (wetter) conditions in early autumn of the warm (cold) episode years and wetter (drier) conditions from winter to spring of the following year. For both regions, the spatial coherences are over 92% (82%) and the temporal consistencies are 71% (75%) during the El Nino (La Nina) events. In addition, for the core regions identified by composite-harmonic analysis for both extreme episodes, the results of comparative analyses by using correlation, annual cycle, and Wilcoxon rank sum test indicate that 2 opposite phases-streamflow relationships have a tendency of sign reversal of the streamflow anomaly. Also, the positive departures during the El Nino years show more coherent and strong responses than the negative anomalies in the La Nina events. In conclusion, South Korea experiences climatic teleconnection between ENSO forcing and midlatitude streamflow patterns.