SUMMER is the busiest time of the year for staff at the Mogao Grottoes, as more than one-third of the annual visitors to the UNESCO World Heritage site arrive during the high-volume vacation season.

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

Located in Dunhuang, Northwest China’s Gansu Province, the Mogao Grottoes’ 735 caves are home to a priceless collection of Buddhist artwork — more than 2,000 colored sculptures and 45,000 square meters of murals — all created by ancient worshippers.

However, only about 110 caves are open to visitors.

“Too many visitors will raise the temperature, humidity and concentration of carbon dioxide in the cave, leading to the repeated dissolution and crystallization of salt. This will cause the murals to decay,” says Su Bomin, vice president of the Dunhuang Academy, the organization that manages the grottoes.

Therefore, multiple measures have been taken to preserve the paintings. In 2014, the academy opened a ticket reservation service and curbed the number of daily visitors. This summer, it has set a cap on the number of visitors of permitted entry every hour between 8 a.m. and 3 p.m., and no more than 12,000 tourists who have not booked tickets in advance are allowed to enter.

“The new measure has significantly lowered the capacity pressure at the site,” says Li Ping, a member of the academy.

Scientific preservation

Over the years, countless antiquarians and experts have devoted their lives and careers to the protection and restoration of the cultural relics in a bid to delay their aging.

Li Yunhe, 86, has been repairing and restoring the ancient grottoes since the 1950s.

“I have repaired over 4,000 square meters of murals and more than 500 colored sculptures,” says 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.

At present, the meteorological environment, cliff conditions, and possible natural disasters such as floods and earthquakes as well as the interior environment of the caves are all under close surveillance. Tourists are asked to depart once the temperature, humidity and carbon dioxide density threaten to exceed safe levels.

“All the data is automatically recorded every 15 minutes. We are studying the relationship between this data and the rate of the decay to continue exploring appropriate preventive measures,” says Guo Qinglin, head of the academy’s conservation institute.

In recent years, extreme weather has posed new threats to the grottoes. Rainfall recorded at the grottoes in July was the most since 1989, when the academy first began keeping records of precipitation.

Thanks to a flood-control structure built in 2013, the downpours now cause only limited damage to the grottoes.

Digital push

Despite all the efforts of the academy, the knowledge that these ancient grottoes will inevitably vanish some day is frustrating.

However, the digitization of the Mogao Grottoes is currently underway, a project that will permanently preserve its glory.

By visiting the Digital Dunhuang website, visitors can immerse themselves in the images of more than 4,430 square meters of murals that span 30 caves.

The database is the result of more than three decades of work. In the 1980s, Dunhuang Academy China began partnering with research institutes and universities, including China’s 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 mural of 300 square meters. “Now we have collected the digital data of 180-plus caves,” says Yu Tianxiu, who is leading the digitization work.

So far, the website has welcomed over 5 million visitors.

“We’ve tried many methods to bring the grottoes to life,” says Fan Jinshi, honorary president of the academy. “We hope that the whole world will see the beauty of the Mogao Grottoes through Digital Dunhuang.” (Xinhua)