A study for the distribution characteristics of surface temperature and the protection of grotto temples in China.

Temperature accelerates the deterioration processes affecting grotto temples. As such, studies of the temperature distribution characteristics of grotto temples can provide an important basis for their protection. In this paper, the hourly surface temperatures of 123 grotto temples in China were studied using ERA5-Land hourly data from 1981 to 2020, obtained through the AI Earth platform. Using the local Python development environment, the daily surface temperature difference and highest and lowest temperatures of grotto temples were linearly fitted for each year, after which the monthly average temperature difference distribution was statistically analyzed to determine trends in temperature change. Then, the GIS Spatially Constrained Multivariate Clustering method was used to cluster the surface temperature characteristics. The results showed that the grotto temples in China can be mainly divided into seven regions, namely Xinjiang, Qinghai-Xizang Plateau, Hexi, Longdong, Shaanxi and North China, Southwest, and East and Southeast. The highest average surface temperature, greater than 15 °C, occurred in South China, and the lowest, close to 0 °C, occurred in the Qinghai-Xizang Plateau. The average surface temperature of the seven regions identified showed an increasing trend. The Qinghai-Xizang Plateau was affected by severe temperature differences throughout the year, with annual average daily temperature differences approaching 30 °C, followed by Xinjiang and Hexi region, with a perennial temperature difference of approximately 25 °C. The Longdong, Shaanxi, and North China regions had annual average daily temperature differences of 15-20 °C, whereas values for the South China region were less than 15 °C. The daily surface temperature differences of grotto temples reached their maximum values in April to May and their minimum values in December to January. All studied regions are subject to temperature-induced challenges: Xinjiang region faces particularly severe high-temperature influences, with a mean daily surface temperature of almost 45 °C in summer, followed by Hexi region with 35 °C or above, and the other regions with approximately 30 °C. The Qinghai-Xizang Plateau exhibits perennially low temperatures, with a mean daily minimum temperature below - 25 °C in winter; less than - 10 °C in the Xinjiang, Hexi, Longdong, Shaanxi, and North China regions; and approximately 0 °C in southern China. The relative impacts of temperature on grotto temples in each region are as follows: Xinjiang and Hexi > Qinghai-Xizang Plateau > Longdong, Shaanxi, and North China > Southwest China > East and Southeast China. This study has revealed the characteristics of surface temperature distribution in grotto temples in China and proposes appropriate protection measures, which will help improve national-scale practical mitigation of the threats facing these important cultural heritage sites.