Climate Change a Threat to Ancient Grottoes
Dunhuang, an oasis city in western China, receives just several centimeters of rainfall per year. The city’s Mogao Caves, the largest collection of Buddhist artwork in the world, has been preserved for more than a thousand years in the arid climate at the edge of the Gobi Desert.
But rainfall patterns in Dunhuang are changing. In a 23-hour period on June 6 and 7 the Mogao Caves received more than 40 mm of rain, just two millimeters shy of the average for an entire year.
The road to the caves was flooded out, and the Dunhuang Research Institute announced their temporary closure, preventing 10,000 scheduled visitors from accessing the site. At the caves, the rainstorm caused falling rocks and some water damage.
Less than two weeks later, Dunhuang saw another 20 mm of rainfall. The caves were once again shut for the day over concerns that high humidity levels posed a threat to the paintings.
While no single rainfall event can be attributed to climate change, data collected over decades indicate that the climate of western Gansu is shifting from dry to wet. Measurements taken at the Dunhuang Weather Station show that rainfall has more than doubled since the 1950s, creeping up by an average of 4.5 millimeters per decade. Precipitation in the nearby Qilian Mountains, the origin of Dunhuang’s Dang River, has increased even more, at a rate of more than 12 mm per decade.
According to state news agency Xinhua, as rainfall increases, the grottoes face “unprecedented” challenges. Changes in humidity can cause salt in the rock and plaster behind the paintings to recrystallize and can encourage the growth of mildew and other microbes. To protect the grottoes, they are closed to visitors if humidity levels rise above 63%.
“Although the impact of rainfall on the grottoes needs to be further observed, it is definitely detrimental to their conservation,” Guo Qinglin of the Dunhuang Academy China told Xinhua.
Impacts of climate change are visible elsewhere in Gansu province. Hexi, the area west of the Yellow River, has seen the most rainy days this year since 1961. At the same time, eastern Gansu is drying out, with draught days on the rise and rainfall increasingly scarce.
In a dry climate with steep terrain and little vegetation, even relatively small storms can cause severe damage.
The same July 7 flood that affected Dunhuang caused the collapse of 93 buildings and destroyed 90 hectares of crops and 9.2 kilometers of road in one Guazhou County village. A video posted online shows the wall of a house collapsing into a flood of rushing water.
Last year flooding in Gansu killed at least 15 people. In Dongxiang county, south of the provincial capital, 2,400 people were evacuated due to flash flooding and mudslides following days of heavy rain.
In Dunhuang itself, flood prevention measures have helped to protect the caves from damage. But given projections that precipitation in western Gansu will continue to rise, a region accustomed to just a few centimeters of rainfall per year is facing historic change.
