Evidence that ancient floods "rewrote" civilizations along the Yangtze River
Stalagmites in Heshang Cave, the location of the study
Changes in temperature and water availability have long since played a significant role in the trajectory of human civilizations. A major climate event around 4,200 years ago (known as the “4.2 kyr event”), which coincides with the decline of major ancient societies, has attracted considerable scientific attention. In China's middle Yangtze River region, the once-flourishing Shijiahe culture collapsed during this period. The reasons behind the abandonment of the ancient Shijiahe city and the abrupt disruption of its cultural development have been widely debated. Now a research team, including Christopher Day and Gideon Henderson from Oxford Earth Sciences, has shown that this collapse was caused by widespread flooding in the middle Yangtze Valley. These findings were published this week in National Science Reviews.
By analysing a stalagmite from Heshang Cave in the middle Yangtze Valley, the research team were able to create a precisely dated "rainfall yearbook". Stalagmites grow as rainwater water drips from the roof of a cave, and the dissolved minerals within add new layers of calcium carbonate to these stalagmite cave features that rise up from the floor below. The team performed high-precision measurements on the chemical makeup of these layers to determine their age and the amount of rainfall at the time they formed. A total of 925 sample measurements were used to infer how much yearly rainfall the middle Yangtze Valley received over a thousand year period.
Heshang Cave, in the middle Yangtze River valley
Their new reconstruction showed that the valley experienced three low-rainfall intervals (less than 700 mm of rain per year) which lasted between 40 and 150 years, and two high-rainfall intervals (more than 1,000 mm per year) which lasted 80 and 140 years respectively. Comparing this to archaeological data from the region revealed that these high-rainfall periods were associated with increased flooding, widespread wetland expansion, and a significant decline in population within the valley.
The HS4 stalagmite, which was used to create the "rainfall yearbook"
The area experienced a particularly large climate and cultural shift 3,950 years ago, which coincided with the start of the longest high-rainfall interval reconstructed by the research team. During this period, excess rainfall caused lakes across the Middle Yangtze valley to expand, low-lying areas to become waterlogged, and suitable land for settlement and farming to sharply diminish. The impact of this change was significant for the Shijiahe culture; a decline in the number of archaeological remains starting at this time indicates a pronounced drop in population which persisted for centuries. Evidence suggests that the post‑Shijiahe population abandoned their urban centre in the valley and dispersed into surrounding higher‑elevation regions.
This study offers valuable insights for addressing current and future environmental change. The analysis reveals that even the peak precipitation during the high-rainfall period associated with the collapse of the Shijiahe civilization was lower than some extreme rainfall events observed in the modern instrumental record.
“This not only reflects the limited adaptive capacity of ancient societies, but also highlights the critical importance of modern day water management infrastructure, agricultural innovations, and governance systems in mitigating climate risks and safeguarding food security. Effectively managing these climate-driven extremes will thus become an essential challenge for achieving sustainable societal development in a climate-changing world.”
- Dr. Jin Liao (China University of Geosciences, Wuhan), lead author of the study
The study “Precise chronology of hydrological changes at ∼4.2 kyr in Central China to assess the impact of flooding on Neolithic societies” is available to read in the journal National Science Review at https://doi.org/10.1093/nsr/nwaf567. This work was conducted in collaboration with Dr Jin Liao, Prof Chaoyong Hu, and Prof Yuhui Liu from the China University of Geosciences (Wuhan).
