Extreme flood events on Western Sakhalin and their linkage to cyclogenesis activity in the western North Pacific in middle-late Holocene

This study provides insights into the natural variability of flood events in the past and the role of large-scale atmospheric circulation patterns in shaping flood patterns. The geological record of extreme floods associated with the passage of the strongest typhoons and deep extratropical cyclones over the past 6370 years has been reconstructed in Western Sakhalin (the Yablochnaya River Basin). A section of peat bog with numerous loam layers formed during extreme floods was used for the reconstruction. A recent analog of such events is typhoon Phyllis (1981 CE), which produced up to 300 mm of rainfall. The analysis of ash content (i.e., non-organic content) in peat, combined with the age-depth model, allows for identifying of 38 past flood events and periods of weaker floods when organomineral sediments accumulated. During active cyclogenesis periods, extreme floods were frequent once every 10–30 years. The analysis of paleoclimatic conditions provides insights into the climate factors contributing to flood risk. Long-term periods with extreme floods were identified as 6470–5490, 4300–3670 yr BP according to the age-depth model. During the last 3110 years, severe floods were rare events. We compare the records of strong floods from the western and eastern coasts of South Sakhalin and different East Asian regions. Periods with frequent strong paleotyphoons and deep extratropical cyclones show different temporal variations in the regions, which could be due to variance cyclone trajectories determined by the anomalies of baric fields. Intensification of the warm Kuroshio Current, which plays a major role in meridional heat and moisture transport, was also a driver of cyclogenesis activation and extreme flooding in southern Sakhalin Island. At present, the increase in the intensity of cyclogenesis and the frequency of typhoons in the middle-late Holocene was closely related to the western Pacific warm pool in the western equatorial Pacific, manifestation of El Niño and anomalies of atmospheric centers of action. This information enhances our understanding of flood history and provides valuable insights for flood risk assessment and climate change adaptation strategies.