Inside the Dayu cave. Image: L.Tan 

The area receives around 70 percent of its rainfall from the summer monsoon in which torrential rain is the dominant weather pattern over the course of a few months. Changes in the timing of the monsoon as well as its duration have major effects on the local ecosystem and it is clear that in times past this in turn led to severe starvation and social instability. In 1900, this also led to fierce conflict between the local population and the Chinese government, while in 1528 the drought was so severe that it may have led to incidences of cannibalism.

"In addition to the obvious impact of droughts, they have also been linked to the downfall of cultures -- when people don't have enough water, hardship is inevitable and conflict arises” Dr Sebastian Breitenbach of Cambridge's Department of Earth Sciences told Science Daily. “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 last 1800 years, such as the Tang, Yuan and Ming Dynasties.”

According to Dr Liangcheng Tan of the Institute of Earth Environment at the Chinese Academy of Sciences in Xi'an, the lead researcher on the project, this is the first time that inscriptions have been found on the wall of a cave relating to drought. The teams investigation, combined with chemical analysis of stalagmite formations within the cave, have led to an increased awareness of the importance of developing measures to counter present and future climate change impacts. It is the first time that it has been possible to conduct an in situ comparison of historical written records with geological formations at the same location. This in turn has enabled the team to gain an awareness of what may happen in the region as rainfall patterns are reduced and droughts are increasingly common.

When stalagmites are cut open, they often display a series of layers much like a tree ring. Mass spectrometry can then be used to analyse and date the ratios of the stable isotopes of oxygen, carbon, uranium and other elements. Given that these elements are affected by local precipitation levels and surrounding vegetation, on the basis that the water in the cave is related to the water outside, scientists have been able to determine that higher oxygen and carbon isotope ratios correspond with lower rainfall levels, and vice versa. The team has now used this information to construct a model of future precipitation, starting in 1982 and correlating with a drought in the 1990’s. This in turn has enabled the scientists to predict a future drought, probably in the late 2030’s.

The droughts also correspond with the El Niño-Southern Oscillation (ENSO) cycle which itself is also widely suspected of being exacerbated by climate change.

"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” added Dr Breitenbach. “Things in the world are different from when these cave inscriptions are written, but we're still vulnerable to these events -- especially in the developing world.”