3D tech, air curtains help Chongqing’s grotto art to adapt to climate change

Rock cavings in Beishan Mountain, an important part of UNESCO Dazu Rock Cavings World Heritage in Chongqing Photos: Lou Kang/GT

 
After undergoing emergency conservation, the state of the thousand-year-old grottoes in Southwest China's Chongqing has stabilized more than ever before. In recent years however, the impact of extreme weather caused by climate change has posed new challenges for the experts: how to keep these grottoes' art stay with us on a journey toward sustainability?

In mid-August, an international forum on the impact of climate change on grotto art was held here, discussing the changes and solutions for the grotto art in Chongqing and beyond under this major factor. 

Chongqing Municipality boasts the largest concentration of grottoes in the region, with over 100,000 large and small cave statues dating back to a thousand years ago. 
Chen Huili, a renowned expert on the subject, told the Global Times that the tricky point for grotto conservation is that "We have no way to change any external conditions, so we need to adapt to environmental changes."

Chen took the example of the Thousand-Hand Guanyin Buddha statue, a masterpiece of Southern Song (1127-1279) Chinese grottoes art that she restored for eight years.

"After finishing the emergency restoration, when others think that it can be done once and for all, we actually have more to do behind. In Chongqing, the biggest threat to the grottoes is humidity, and with the increase of extreme weather, more and more floods and rainfall will increase the humidity of the air around the grottoes," she said.
"When humid air meets the dense sandstone material of the grottoes, acid forms on the statues, corroding the statues and causing irreversible damage."

At present, experts told the Global Times that they have proposed some solutions based on technology: a real-time monitoring system, 3D laser scanning and an air curtain that is being developed.

The first two have been put into use in all grotto scenic areas in Chongqing, while the third is still at the research stage, being developed in cooperation with Tsinghua University in Beijing.

"After being put into use, the air curtain will form an invisible purification barrier around the grottoes on the cliff face, filtering out pollutants that may harm the surface of the grottoes, and lengthening their life span to the greatest extent," Chen told Global Times.

In fact, the conservation of grottoes began decades ago.

Rescue and restoration

For many visitors, the Dazu Rock Carvings evokes memories of another World Heritage site in Cambodia: Angkor Wat. Due to their similar geographical and climatic conditions and carving techniques, many people may feel a sense of deja vu when visiting both sites.

The grottoes in Chongqing were first carved in the Tang Dynasty (618-907), initially by local gentry and officials for prayer and worship. In the following thousand years, the local residents passed down this tradition and began to carve large and small statues on the mountains seeking children and blessings. Until now, the smell of sandalwood incense around the Chongqing grottoes is very strong, and people continue to light sticks of incense and leave their good wishes there.

The surrounding environment was once the biggest threat to the grottoes: the air pollution from factories in the area, sudden rainfalls and the prolonged exposure to the sun that brought irreversible threats to the color of the grottoes' surface.

To solve these problems, in 1952, Dazu established a research institute for emergency protection of rock carvings. In the past few decades, heavily polluted industries have moved away from the surroundings, tunnels have been built to divert floods away from the grottoes and cracks have been repaired.

Jiang Siwei, director of the Dazu Rock Carvings Research Institute, told the Global Times that the current rock carvings protection has tended to be stable, but that is not over as the threat of extreme weather to the grottoes has always been there.

According to a report on natural disasters in 2022 published by China's Ministry of Emergency Management in 2023, a total of 5,659 geological disasters such as landslides, collapses and mudslides occurred mainly in central south and southwest China.

At the same time, droughts are also increasing. The report shows that six regions, including Chongqing, accounted for 70 percent of forest fires in China in 2022.
Experts told the Global Times that they have adopted the most primitive physical method to regulate air: by controlling the types of vegetation around, they can well maintain the balance of air humidity and achieve good results.

Before more technological means are researched out, "What we have to do is real-time monitoring and observation," Jiang told Global Times.

Due to the wide distribution of grottoes, the research institute hired local villagers after training sessions and let them take on part of the responsibility for protection.
"The villagers'responsibility is to ensure that the grottoes are not robbed. At the same time, our professional staff will inspect them every day and repair them in time when they see cracks and weathering."

Digital technology helps

In addition to Chongqing's Dazu Rock Carvings, China's other four major grottoes, which are treasure troves of ancient art and culture, are also facing environmental threats and in need of technology for protection and research. The grottoes include the Yungang Grottoes, the Mogao Caves, the Longmen Grottoes and the Maijishan Grottoes, all of which are UNESCO World Heritage Sites. 

According to Sixth Tone, Dunhuang in Northwest China's Gansu Province, a key exchange point on the Silk Road, has seen a sharp rise in short-term heavy rainfall days since 2000, based on local weather data. 

To save these precious relics, the Dunhuang Research Institute has launched a "Digital Mogao Caves" project, which has digitized 289 out of 492 caves in the Mogao Caves over 30 years. 

The project has also created 3D models of 45 colored sculptures, 140 caves, and seven large sites, as well as 162 panoramic tours of the caves. Moreover, more than 50,000 archive negatives have been digitized for permanent preservation and sustainable use. For experts, this is perhaps the best way to preserve the grottoes to keep China's ancient diversity and heritage.