Guo Qinglin, director of the Dunhuang Academy, recalled how recent summer downpours flooded cave entrances and sent humidity levels soaring inside. "The threshold is 62 percent," he said. "Above that, salts in the plaster layers deliquesce, and the relics begin to decay from within."

　　Rain, sand, or shine -- the doors respond, said Wang Xiaowei, director of the Dunhuang Academy's cave monitoring center. "They seal out moisture during the rain, lock tight against blowing sand and open to ventilate on clear days, optimizing the internal environment with every shift in weather."

　　These smart doors have been installed in select caves at Mogao and the Western Thousand-Buddha Caves.

　　The system runs on real-time data from over 600 sensors placed in and around the grottoes. The monitoring center's big screens display everything in real time: cave temperature, humidity, carbon dioxide levels, visitor flow, and even rainfall and sandstorms across hundreds of kilometers around.

　　A red-yellow-green alert system flags danger. "When extreme weather hits, we stop ticket sales and seal the doors, cutting off moisture before it can reach the murals. Every closure buys the paintings more time," Wang said.

　　To get ahead of potential risks, researchers at the Dunhuang Academy's lab can simulate a range of weather conditions, from minus 30 degrees Celsius to 60 degrees Celsius, along with wind, rain, snow and sunlight.

　　"Time can be 'accelerated' in this facility," Guo said, noting that a full annual cycle can be recreated in just 40 to 50 days in the lab. This allows the team to "preview" how relics will age in the wild and, with that foresight, craft preservation strategies before any real damage occurs.