报告题目：Deciphering flood magnitude in alluvial sediment record
沈治雄，博士，现任美国海岸卡罗莱纳大学海洋科学系副教授。2002年毕业于北京大学，获理学学士学位，2007年毕业于利物浦大学，获博士学位，曾于2007年至2014年在杜兰大学从事科研工作。研究兴趣包括地表过程、环境变化、海平面变化、第四纪年代学、河流和与海岸地质，在《GSA Bulletin》、《Geology》、《JGR-Solid Earth》、《AGU Advance》、《Nature》、《Science Advance》等期刊发表多篇论文，获得过多项美国国家科学基金资助。
Extending the history of extreme floods beyond instrumental records is critical for understanding their climatic and anthropogenic forcing. Alluvial sediments are produced by riverine flooding and thus preserve the flooding history. Observation of extreme-flood deposits suggests that these floods do not always produce distinctive sedimentary records, challenging the idea of using alluvial records to reconstruct flood magnitude. Here I present a comprehensive study of recent 50- to 100-year floods in the Great Pee Dee River system on the US Atlantic Coast. The results show that the event deposits can be distinctly coarser and thicker than average-size floods but depends on factors such as location, hydrological connectivity, and sediment source. We find strong correlations between the coarseness of event deposits and flood magnitude at multiple sites, suggesting that alluvial sediments can be greatly useful for paleoflood reconstruction. We reconstructed the flooding history of the Great Pee Dee River over the past ~200 years using alluvial sediments. It shows that the magnitude of extreme floods has reduced dramatically during the past 70 years in comparison with the late 19th to early 20th century, strongly corroborating a limited number of instrumental records in the southeastern US. This decrease in magnitude is due to climate change, land-use modification, and river damming. Our result indicates that the magnitude of extreme flooding in major rivers decreased despite an increase in frequency and intensity of extreme precipitation in the southeastern US over the last century, suggesting a complex interplay between inland flooding, human activity, and heavy precipitation.