Discover China: Let the dying never die - China's efforts to preserve ancient grottoes

Summer is the busiest season for staff at the Mogao Grottoes, as more than a third of the annual visitors to the over 1,650-year-old UNESCO World Heritage site come during summer vacation.

Last year, the tourist attraction welcomed almost 2 million visitors.

Sitting in Dunhuang, northwestern China's Gansu Province, the Mogao Grottoes are home to a priceless collection of Buddhist artwork -- more than 2,000 colored sculptures and 45,000 square meters of murals -- in 735 caves carved along a cliff by ancient worshippers.

But only about 110 caves are suitable for visiting. "Too many visitors will affect the temperature, humidity and concentration of carbon dioxide in the cave. This will lead to repeated dissolution and crystallization of salt in the cave, causing the murals to decay," said Su Bomin, vice president of Dunhuang Academy China, which manages the grottoes.

Multiple measures have therefore been taken to preserve the works. In 2014, it took the lead to open ticket reservations and curb the number of daily visitors. This summer, it set a cap on the number of visitors every hour between 8 a.m. and 3 p.m. where no more than 12,000 visitors that did not book tickets in advance are allowed to enter.

"The new measure has significantly lowered the capacity pressure of the site," said Li Ping with the academy.

SCIENTIFIC PRESERVATION

In the meantime, countless antiquarians and experts have devoted their whole life to the protection and restoration of the cultural relics, to delay its aging.

Li Yunhe, 86, has been repairing ancient grottoes at Dunhuang since the 1950s. "I have repaired over 4,000 square meters of murals and more than 500 colored sculptures," said Li. "I have to keep updating my techniques to better restore the cultural relics."

A monitoring and early warning system also plays a key role in its conservation.

The Mogao Grottoes began monitoring the nearby environment as early as the 1960s. In 1989, a meteorological station was set up and in 2011, the current monitoring system was put into use.

Now the meteorological environment, cliff conditions, possible natural disasters such as floods and earthquakes as well as the interior environment of the caves are all under close surveillance, with the site becoming closed to tourists once the temperature, humidity and carbon dioxide density threaten to exceed safe levels.

"All the data are automatically recorded every 15 minutes. We are studying the relationship between these data and the rate of the decay to explore appropriate preventive measures," said Guo Qinglin, head of the academy's conservation institute.

Extreme weather in recent years has also posed new threats to the grottoes. In July this year, the grottoes saw the biggest rainfall since 1989, when the academy began tracking records of precipitation.

Thanks to the flood control project constructed in 2013, the downpours caused only limited damage to the grottoes.

INVIGORATED WITH MODERN TECHNOLOGY

Despite all the efforts, it is frustrating that these ancient grottoes will inevitably vanish some day. But a digitalized Dunhuang Mogao Grottoes which is under construction will permanently preserve its glory.

By visiting the website "Digital Dunhuang," visitors can be immersed in the images of more than 4,430 square meters of murals across 30 caves.

The database was a result of more than three decades' endeavor. In the 1980s, Dunhuang Academy China began partnering with research institutes and universities including Zhejiang University and Northwestern University in the United States to digitalize the ancient cultural relics.

At least 40,000 photos must be taken to digitalize a 300-square meter mural. "Now we have collected the digital data of 180 plus caves," said Yu Tianxiu who leads the digitalization work.

Technologies such as immersion display and virtual interaction used in the display and preservation of the Dunhuang Mogao Grottoes have also been applied to support the conservation of ancient heritage sites in countries along the Belt and Road.

Now the webiste has seen over 5 million visits. "We've tried many methods to let the grottoes come alive," said Fan Jinshi, honorary president of the academy. "We hope that the whole world can see the Mogao Grottoes through 'Digital Dunhuang.'"