Abstract: The Qinghai-Tibet Plateau has a unique location, complex landform, and rich resources, with essential climatic regulation, ecological security, and special geographical significance for China and even the world. The assessment of ecological quality changes on the Qinghai-Tibet Plateau is of great significance for regional ecological protection and global change research. Based on the Google Earth Engine, we constructed a remote sensing ecological index (RSEI) by combining regional characteristics. We further analyzed the spatiotemporal variations of ecological quality in the plateau from 2000 to 2020, and examined the responses of ecological quality to climate changes and land use changes. The results showed that ecological quality had been generally improved and partially deteriorated, of which 68.33% had increased significantly, mainly distributed in Qinghai and Tibet, and 4.39% had decreased significantly, mainly located in Xinjiang and some parts of southern Tibet over the past 20 years. The RSEI was relatively low, with an average of 0.40, and showing an upward trend from the northwest to the southeast. The coefficient of variation of RSEI was dominated by weak and relatively weak grades, accounting for 89.33% of the total area, indicating that its variability could be negligible. The mean value of Hurst index was 0.45, indicating that the future change trend of ecological quality is stronger in reverse than in same direction, showing a weak deterioration trend in the plateau. Among them, 0.28% of the area with significant continuous deterioration was located in the northwestern plateau. Only 12.40% of the plateau that will begin to deteriorate was mainly distributed in the central and northern plateau. The impacts of precipitation on RSEI were greater than that of temperature. The area with significant correlation between RSEI and temperature only accounted for 10.68%, while that with significant correlation between RSEI and precipitation accounted for 25.73%. The improvement and expansion of forest and grassland promoted the improvement of ecological quality, while the reduction of permanent glaciers and snow led to the deterioration of regional ecological quality. Our results can provide a theoretical basis for regional ecological restoration and promoting ecosystem balance of Qinghai-Tibet Plateau.

Key words: Qinghai-Tibet Plateau, remote sensing ecological index, ecological quality, spatiotemporal variation, Google Earth Engine.