Located on the southern slope of the Qinling Mountains in central China, Dayu Cave is home to ancient inscriptions that paint a picture of the societal impacts of climate change over seven major drought events between 1528 and 1894.
“In the past decade, records found in caves and lakes have shown a possible link between climate change and the demise of several Chinese dynasties during the past 1,800 years, such as the Tang, Yuan and Ming Dynasties,” said Sebastian Breitenbach, of the Univ. of Cambridge’s Dept. of Earth Sciences.
According to the researchers, whose work is documented in Scientific Reports, the region is “dominated by the Asian monsoon system, with a mean annual rainfall of 1,100 mm.” Seventy percent of that amount is received during the monsoon months between June and October, when the cave’s aquifer is recharged.
An inscription from 1891, a year of a main drought event, reads, “the local mayor, Huaizong Zhu, led more than 200 people into the cave to retrieve water. A fortuneteller named Zhenrong Ran prayed for rain during the ceremony.” Three years later, during another drought period, the process was repeated, but with 120 people.
“The inscriptions describe the event as ‘mountains are crying due to drought,’ and local people ‘came to the cave to get water’ in July and August when the summer monsoon is presumably the strongest,” the researchers write of a drought period during the 16th and 17th centuries.
Societal effects include starvation and acts of cannibalism in the mountain region, from the Shaanxi Province to the eastern Gansu Province, during the drought of 1528, according to researchers. In the 1890s, droughts once again led to severe starvation and social instability, which resulted in conflict between government and civilians in 1900.
“Since the Qinling Mountains are the main recharge area of two larger water transfer projects, and the habitat for many endangered species, including the iconic giant panda, it is imperative to explore how the region can adapt to declining rain levels or drought,” said Breitenbach. “Things in the world are different from when these cave inscriptions (were) written, but we’re still vulnerable to these events—especially in the developing world.”
According to the researchers, the inscriptions helped form a link between past droughts and the geochemical record of the cave. Utilizing mass spectrometry, the team cut open cave formations, such as stalagmites, for a glimpse into the cave’s past conditions, and analyzed the isotope ratios of oxygen and carbon. Higher oxygen and carbon isotope ratios correlated with lower rainfall levels, the researchers found.
Using their data, the researchers created a model of future precipitation starting in 1982. Two droughts, one forecasted in the 1990s, which was confirmed by instrumental data, and another in the 2030s were predicted.
If warming continues, the researchers say, precipitation may decrease in the cave region.
Precipitation in the region is responsible for the recharge of the Danjiangkou Reservoir, which supplies the middle route of the South-to-North Water Transfer Project, designed to carry 44.8 billion cubic m of water per year. The region’s Hanjiang-to-Wihe River Water Transfer Project is under construction.
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