Floods and Climate Changes on the Western Coast of the Japan Sea in the Late Holocene: Reconstructions Based on Geochemical Proxies, Role in the Collapse of the Bohai State

In recent decades, catastrophic river floods have become more frequent on the western coast of the Japan Sea, including the territories of northeastern China, southeastern Russia, and northern Korea. Climate change and anthropogenic interference into riverbed processes are considered as possible causes of this. The aim of the work was to assess the role of climate change using reconstructions of the frequency and intensity of floods over the past millennia in the basin of one of the rivers. According to the submillimeter scanning of shelf sediments of the Amur Bay on the X-ray fluorescence analysis using synchrotron radiation, the frequency and intensity of floods in the late Holocene were reconstructed. The predominant role of typhoons (tropical hurricanes), the possibility of penetration of which into the region increases during warm periods, is substantiated as the main cause of floods on the coastal rivers. Due to this, the dependence on changes in air temperature and solar insolation in summer has been shown in variations in the frequency and intensity of floods in recent millennia. Accordingly, a long-term trend of their decrease has been established, but after the end of the cold Little Ice Age, with an increase in air temperature, the frequency and intensity of floods in the 20th-21st centuries AD began to increase. This was recorded by hydrometeorological observations and served as the basis for pessimistic forecasts for the future. The example of the medieval Bohai State in the 10th century AD shows the impact of climate change, floods and other natural disasters on human economic activity in climate conditions close to modern ones.