Some 4,000 years ago, a sophisticated society that built a city of canals known as “China’s Venice of the Stone Age” abruptly vanished. Historians have long debated whether war, disease or famine caused the Liangzhu culture’s collapse. Now, they’ve pinpointed a key culprit in the civilization’s fall: climate change.
According to Ellen Phiddian of Cosmos magazine, researchers determined that an unusually heavy series of wet monsoons flooded Liangzhu City, forcing residents to abandon their homes. Writing in in the journal Science Advances, the team details how an overactive El Niño cycle likely resulted in massive flooding and the collapse of the community’s intricate infrastructure.
“The massive monsoon rains probably led to such severe flooding of the Yangtze [River] and its branches that even the sophisticated dams and canals could no longer withstand these masses of water, destroying Liangzhu City and forcing people to flee,” says study co-author Christoph Spötl, head of the Quaternary Research Group at the University of Innsbruck in Austria, in a statement.
Located about 100 miles southwest of Shanghai on an estuary near the East China Sea, Liangzhu was inhabited by an advanced Stone Age civilization for about 1,000 years, from roughly 3300 to 2300 B.C.E. The society built an elaborate network of canals, dams and reservoirs that supported an active agricultural system, reports Alexandra Mae Jones for CTV News.
Archaeologists discovered the ruins of the city in 1936 and have been puzzled by its seemingly sudden demise ever since. Per the Smithsonian’s National Museum of Asian Art, excavations have uncovered a wealth of artifacts at the site, including intricate jade carvings. Liangzhu City was listed as a Unesco World Heritage Site in 2019.
Researchers had previously speculated that flooding was the reason for Liangzhu’s abandonment but had little proof to support this hypothesis.
“A thin layer of clay was found on the preserved ruins, which point[ed] to a possible connection between the demise of the advanced civilization and floods of the Yangtze River or floods from the East China Sea,” says Spötl in the statement. “No evidence could be found for human causes such as warlike conflicts. However, no clear conclusions on the cause were possible from the mud layer itself.”
A break in the case arrived when scientists started examining stalagmites from two nearby underwater caves. As Peter Dockrill reports for Science Alert, they discovered chemical signatures from about 4,300 years ago that showed extremely high precipitation, probably caused by the warming of ocean waters in the Pacific—an event known as the El Niño–Southern Oscillation.
“These caves have been well explored for years,” Spötl states. “They are located in the same area affected by the Southeast Asian monsoon as the Yangtze delta and their stalagmites provide a precise insight into the time of the collapse of the Liangzhu culture.”
According to Cosmos, researchers used carbon isotope analysis to determine humidity when the stalagmites were formed and uranium-thorium dating to estimate their age. The data showed a period of excessively heavy rains between 4,345 and 4,324 years ago, plus or minus 30 years.
“This is amazingly precise in light of the temporal dimension,” says Spötl in the statement.
The study notes that wet conditions lasted for several hundred years following the abandonment of Liangzhu, eventually paving the way for the rise of the Xia dynasty in 2070 B.C.E. Its reputed founder, Yu the Great, introduced more extensive flood-control methods and is known as the “Tamer of the Flood.”
“While many documents indicate that the leader Yu built the Xia dynasty because he successfully managed river flooding, some studies suggest that Yu’s control of the flooding can be ascribed to climate change,” the authors write, adding, “This observation provides new robust evidence that the rise of the Xia dynasty occurred in the context of a major climate transition from wet to dry.”