BEIJING, Feb. 12 (Xinhua) -- Chinese scientists have recently quantified the correlation between prehistoric human population fluctuations and climate cycles in the lower Yangtze River region, revealing patterns of societal change, according to the Chinese Academy of Sciences' Institute of Geology and Geophysics.

By systematically analyzing chronological data from thousands of archaeological sites, experts from the institute and collaborating institutions identified clear cyclical fluctuations in the region's population size between 10,000 and 3,000 years ago.

Further investigation indicated that this pattern resulted from the interplay of periodic environmental shifts -- driven by changes in the East Asian summer monsoon season -- and the development of human societies. The findings have been published on the Quaternary Science Reviews journal website.

The research team systematically collected and analyzed radiocarbon dating data from 1,008 Neolithic to Bronze Age archaeological sites in the lower Yangtze River region and adjacent coastal areas.

Using a high-precision population dynamics model, a distinct pattern emerged: Over the past 10,000 years, the region's population density did not increase in a linear fashion but underwent marked cycles of expansion and contraction, recurring approximately once every 500 years on average.

Deeper analysis revealed that these demographic cycles corresponded closely to periodic variations in the intensity of East Asian summer monsoons. The study highlights a "seesaw" effect in the influence of these monsoons on rainfall distribution across northern and southern China. Whenever the summer monsoon season weakened, the lower Yangtze River region experienced increased precipitation. The resulting warm and humid climate boosted regional biomass productivity significantly, supporting rice-based agriculture in particular, which in turn provided a foundation for population growth. Conversely, when harsher summer monsoon seasons led to drier local conditions, resource pressures increased and populations contracted.

The research also led to a more profound insight, revealing that population levels remained relatively stable despite ongoing climatic variability between about 7,800 and 5,500 years ago.

"This represents a critical transition, indicating significantly enhanced societal resilience during that period," according to lead researcher Xu Deke.

Xu noted that this resilience stemmed from multiple social advancements: improved agricultural techniques, the diversification of subsistence strategies and the evolution of social organization. During certain phases, these developments allowed human societies to decouple partially from direct climatic constraints through technological and organizational innovation.

The study has also highlighted the profound impact of extreme climate events. For example, it found that exceptionally severe flooding about 4,300 years ago may have exceeded the capacity of the Liangzhu culture's water management infrastructure, contributing to the decline of this remarkable civilization.

"This research not only quantifies the links between prehistoric population dynamics and climate cycles but also illustrates how human societies evolved from passively adapting to the environment to actively building resilience," Xu said.

"It offers a valuable historical perspective for our understanding of the relationship between the rise and fall of civilizations and environmental change, and for our consideration of pathways to sustainable development in the context of contemporary global climate change," he noted.