Extreme flood events in the Yi and Shu river basins of the Haidai region (Shandong Province, China) during the late Holocene: Implications for future risk prediction

Modern floods in the Yi and Shu river basins (YSRs), the largest mountain torrent channels in the Haidai region, Shandong Province, China, are often triggered by monsoonal rainfall, shaping the fluvial landscape through frequent inundations. However, our understanding of flood events remains limited due to short observational records and their limited spatial distribution. The lack of long and complete palaeoflood records limit our understanding of extreme flood events, hindering risk prediction and prevention efforts. In this study, we examine the sediment characteristics of two palaeoflood profiles in the YSRs and, based on twelve optically stimulated luminescence (OSL) ages, four ¹⁴C ages, and grain size-sensitive components, identified three exceptional palaeoflood periods: 4.1–3.9 ka, 3.4–2.9 ka, and 0.88–0.7 ka, along with a less severe flood period during 0.7–0.1 ka. An analysis of pollen records, stalagmite data, historical flood records, and El Niño-Southern Oscillation (ENSO) activity reveals a strong correlation between palaeofloods in the YSRs basin and other major rivers (Yellow River, Huai River, Han River, and Yangtze River) with a significant negative correlation to the intensity of the East Asian Summer Monsoon and a positive correlation to the ENSO intensity. These palaeoflood events are typically closely linked to global climate shifts during the late Holocene, including the 4.2 ka event, the 2.8 ka event, and the Little Ice Age. Simultaneous occurrences of climatic deterioration (arid and cold) and palaeofloods during 4.1–3.9 ka and 3.4–2.9 ka may have contributed to cultural disruptions during the Late Longshan Culture period and the decline of the Shang culture in the Haidai area. We argue that these hydroclimatic events are regional expressions of global climate phenomena, and the identified palaeofloods offer key insights into how East Asian rivers respond to global climate change.