Palynological and sedimentological evidence for early mid-Holocene hydroclimatic variability in the Ningshao Plain, East China

The southeastern coastal areas of China represent one of the most populous and economically developed regions in China, but they are often severely affected by flood hazards. Therefore, studying the phenomenon and mechanisms behind extreme rainfall changes in this region is of great significance for economic and social development. In this study, we present high-resolution pollen and grain-size records from the Shanglin Lake located in Zhejiang, eastern China, based which changes in the frequency of paleo-flood events were reconstructed and the climatic context was inferred. Our pollen records show that the content of evergreen broadleaf trees gradually increased during 8000-7000 cal. yr BP, reflecting the gradually increasing temperature in the growing season. The content of Altingia increased substantially during the periods of 7960-7860, 7600-7500, and 7200-7100 cal. yr BP, especially in the first and last periods, indicating the prevalence of an El Nin similar to o-like condition in the study area during the early mid-Holocene warm period. Grain-size record shows that the prolonged El Nin similar to o condition facilitated a significant increase in flood frequency. Our results suggest that, similar to that of today, the early mid-Holocene warm climate was the most important factor controlling extreme hydroclimatic changes in the middle and lower reaches of the Yangtze River.