Climate has always had a voice in human history. When the rains come at the right time, crops grow and cities prosper. If not, people will move, adapt, and sometimes disappear.
About 4,200 years ago, Earth experienced a major climate change. Civilizations from the Middle East to Asia struggled. In central China, the large, organized society known as the Shijiahe culture began to decline.
For years, researchers debated why the ancient city of Shijiahe was abandoned. drought He seemed like an obvious suspect.
A team of scientists has now determined that the cause of the Shijiahe collapse was repeated and prolonged rainfall in the Yangtze Valley. Their findings indicate that overwhelming flooding is a tipping point.
Rainfall written on stone
To understand what happened, researchers went underground. Inside Tsurugami Cave in the middle reaches of the Yangtze River Valley, they studied stalagmites that were slowly growing from the bottom of the cave.
Stalagmites form when rainwater drips from the ceiling, leaving behind a tiny layer of calcium carbonate. Each year, those layers pile up like pages in a history book.
By measuring the chemical composition of these layers, the team created what they called a “rainfall almanac” with precise dates. They performed 925 sample measurements to recreate the amount of rain that fell each year over 1,000 years.
The results were clear. The valley experienced three dry periods, each lasting between 40 and 150 years. rainfall It fell below 700 millimeters (approximately 28 inches) per year.
There were also two very wet periods, one lasting 80 years and the other 140 years, with annual rainfall exceeding 1,000 millimeters (39 inches).
Flooded land, shrinking cities
When researchers compared rainfall records with archaeological evidence, the pattern stood out. Serious signs line up during humid periods floodexpansion of wetlands, and sharp decline in population.
About 3,950 years ago, the region experienced the longest period of heavy rain on record. The lake has expanded. Low-lying areas were flooded. Farmland has shrunk.
At the same time, the number of archaeological sites associated with the Shijiahe culture began to decline. The decline was not short-lived. It lasted for centuries. Evidence suggests that the survivors left the valley’s urban centers and moved to higher ground.
team from School of Earth Sciences, University of Oxford The China University of Geosciences (Wuhan) led the research behind these discoveries. Their research connects climate records from deep within caves to the fate of complex societies above ground.
The amount of rainfall is too much for Shijiahe to handle.
One striking detail stands out. In this study, even the peak precipitation Rainfall during the pluvial period associated with the collapse of the Shijiahe civilization was lower than some extreme rainfall events recorded in modern times.
That’s important. Ancient societies did not have dams, levees, advanced drainage systems, or large-scale flooding schemes.
They relied heavily on stable seasonal patterns. Once these patterns broke down for decades at a time, options were limited.
The Shijiahe culture built large settlements and developed sophisticated crafts and trade networks.
However, they were unable to outstrip the swollen lake, and were unable to fill in the fields that were submerged every year. Over time, moving may become the only viable option.
Lessons for a warming world
This research does more than just explain the collapse of antiquity. This shows how sensitive human systems are to long-term changes in rainfall. Too little water is dangerous. Too much can be equally destructive.
Shijiahe’s story is not just about the past. It’s about limits. extreme climate You don’t need to break records to disrupt society. It just needs to last long enough.
Four thousand years ago, the continuous rain turned into relentless rain. The field was drowned. The city was empty. The culture that once flourished in the middle reaches of the Yangtze River basin has been scattered to the highlands. Crane Shang’s Cave was tracking every drop of water. Now it told the story.
The entire study was published in the journal National Science Review.
Image credit: ©Science China Press
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