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Henan area is climatologically situated in the transition between northern and southern China and the transition is reported to be highly sensitive to climate changes during the Holocene. To better understand the Holocene climatic and environmental changes in Henan area where high-quality data are lacking, this paper first reviewed those published palaeoenvironmental records in attempt to provide a low-resolution framework of the Holocene environmental changes in Henan area, and then synthesized the moisture proxy records from the surrounding areas in attempt to define a high-resolution trend of the Holocene moisture variation for our target site (i.e., Zhengzhou within Henan area). Two major conclusions can be drawn. First, the high-resolution Holocene moisture curve for our target site well follows the general moisture trend of China and the curve is well corroborated by two recently-reported data sets: one from Mangshan loess-palaeosol sequence and another from Laomu-Dongshiya Cave. Second, our synthesis supports an earlier notion stating that the "Holocene Moisture Optimum" in China was a delayed response to the oceanic "Holocene Thermal Optimum". The latter might in turn be a delayed response to the summer insolation peak. [ABSTRACT FROM AUTHOR]

The Central Plains of China witnessed a crucial cultural transformation towards the end of the Longshan period from a chiefdom-like society to a state-level society that has been speculated to be associated with regionally favorable environmental conditions. However, this speculation has not yet been substantiated. We first compiled the information on human migrations and extreme floods during the late Longshan period and then compared the relationships of human settlements with hydrogeomorphic settings in the Central Plains between the Longshan and Xinzhai-Erlitou periods. Our comparison shows that the course of the Yellow River was relatively stable during the Longshan period in the eastern Central Plains, where abundant highlands might have existed for human dwellings. However, geologically and archaeologically documented extreme floods that occurred at ~ 4000 cal. yr BP changed hydrogeomorphic settings in key locations along the Yellow River. The northern Henan area and the bordering area of Henan, Shandong and Anhui Provinces were subjected to frequent crevasses from flooding of the Yellow River at ~ 4000 cal. yr BP, which might have forced human migrations. Consequently, the northern Henan area and the bordering area of the three provinces lacked human settlements, whereas the western Central Plains contained concentrated human settlements during the Xinzhai-Erlitou period. We propose that the success of the above-mentioned cultural transformation was likely causally associated with hydrogeomorphic setting changes in the lower Yellow River Basin. Specifically, the frequent crevasses from flooding of the Yellow River at ~ 4000 cal. yr BP in the eastern alluvial plain regions made the western hilly and mountainous regions of present-day Henan Province the "refuge" for eastern immigrants during the late Longshan period. After the floods, human reoccupation and subsequent population increase beyond the local optimum carrying capacity within the Luoyang Basin during the Erlitou period might be a key driver of local social complexity. [ABSTRACT FROM AUTHOR]