Late Holocene flooding records from the floodplain deposits of the Yugu River, South Korea

Abstract

Predicting responses of regional hydrological cycles to global warming requires an understanding of past hydrological events on various timescales. This study investigated the variability of flooding as recorded in fluvial floodplain deposits. The percentage of sand-sized material in two cores collected from the floodplain of the Yugu River, one of the tributaries of the Keum River, central South Korea, has been tested as a proxy for the occurrence and magnitude of past flooding. The sand fraction of the floodplain deposits in cores KL28 and KL29, which record deposition over the last 3500years, varied on multicentury timescales and suggests several past episodes of higher frequency large floods. These clusters of large floods seem to correlate well with Northern Hemisphere temperature anomalies and suggest that more frequent large floods occurred during the Medieval Warm Period (MWP) than during the Little Ice Age (LIA). The occurrence of more frequent large floods on the Keum River tributary may have been driven by intensified northerly winds over East Asia and resultant moisture convergence over Korea and/or a weakened thermal gradient between the tropical ocean and Asian continent. Furthermore, the centennial-scale changes in the sand fraction of the floodplain deposits were partly similar to remote El Niño–Southern Oscillation (ENSO) activity, implying a possible link between flooding in central South Korea and ENSO activity. This study has demonstrated that floodplain deposits have much potential for recording paleofloods though floodplains can be, and quite often are, very complex places in terms of their depositional history. In regions where natural lakes suitable for the study of paleohydrology and paleoclimate are lacking, well-controlled time-series data for the sand content at multiple sites in fluvial floodplains may be used to understand paleoflooding and extreme precipitation variability in the past.