Approximately 4,000 years ago, a remarkable civilization flourished along the Yangtze River in China, distinguished by its impressive palaces, advanced water management systems, and exquisite jade artifacts. However, this thriving society suddenly vanished.
The cause of the collapse of the Shijiahe culture has long been debated--was it due to invasions or environmental changes? Recent research, however, reveals a surprising culprit: decades of persistent, heavy rainfall.
Scientists have meticulously reconstructed ancient rainfall patterns by analyzing oxygen isotopes and trace elements found in cave stalagmites. This comprehensive record indicates that extended periods of flooding forced the inhabitants to abandon one of Neolithic China's most developed urban centers.
The Era of Excessive Rainfall
Stalagmites, which form as mineral-rich water drips from cave ceilings, preserve a chemical history of the climate above. By extracting numerous microscopic samples from a stalagmite in Heshang Cave, researchers compiled a detailed "rainfall yearbook" for the central Yangtze Valley, conducting 925 measurements to assess annual rainfall from approximately 4,600 to 3,500 years ago.
The findings highlight significant fluctuations in rainfall. Three dry spells recorded less than 700 millimeters of rain annually, while two wet phases exceeded 1,000 millimeters per year and persisted for decades. The most dramatic shift began around 3,950 years ago, marking the onset of the longest wet period.
These prolonged wet decades were accompanied by expanding wetlands, frequent flooding, and a notable decline in population. As lakes expanded and lowlands became saturated, agricultural lands and settlements diminished, severely undermining the agricultural foundation of the Shijiahe region.
Too Much Water, Not Too Much Conflict
Previous theories attributed the societal decline to raids from neighboring groups, but the new evidence aligns the cultural downturn with extreme rainfall events. Population levels peaked between 4,400 and 4,100 years ago, then plummeted as the wet period commenced. Communities gradually abandoned urban centers, relocating to higher ground--a trend that persisted for centuries.
Conversely, dry spells proved less catastrophic. During earlier periods of low rainfall, residents adapted by shifting from water-intensive rice cultivation to drought-resistant millet, maintaining stable populations. While insufficient water can strain a society, excessive rainfall can render the land uninhabitable.
Professor Gideon M. Henderson from the University of Oxford, a co-author of the study, remarked, "The data has allowed us to demonstrate, for one of the first times, that excessive rain can pose challenges for ancient societies, alongside drought conditions."
The collapse of Shijiahe coincided with the 4.2-kiloyear event, a time of global climate disruption often associated with drought-induced declines elsewhere. In this case, however, the evidence indicates that enduring floods--not drought--were the primary factor.
Lessons for Today's Climate Challenges
The reconstructed ancient rainfall data indicated a peak of around 1,200 millimeters per year--intense, yet still lower than some extremes recorded in recent decades. Modern advancements in engineering, irrigation, and governance enable the middle Yangtze region to produce a significant portion of China's rice, a luxury ancient farmers lacked.
Lead author Jin Liao from the China University of Geosciences emphasized, "This not only reflects the limited adaptive capacity of ancient societies but also underscores the vital importance of contemporary water management systems, agricultural innovations, and governance in mitigating climate risks and ensuring food security."
As global temperatures rise, the likelihood of extreme rainfall is expected to increase in many areas. The fate of Shijiahe serves as a reminder that the gradual accumulation of water over time can be just as perilous as drought.
The findings have been published in the National Science Review.
