###### Abstract  
Fractional Vegetation Cover (FVC) is an important indicator to evaluate the quality of the regional ecological environment. Alar City is a typical desert oasis region. Investigating the spatial and temporal changes in its vegetation cover at different stages is a guide to the ecological balance and sustainable green development of the Tarim River basin. Based on the Google Earth Engine (GEE) cloud platform, this study analyzed the spatial and temporal characteristics and trends of vegetation cover changes in Alar City from 1990 to 2020 using the Hurst index and coefficient of variation. The results show that the spatial distribution of vegetation in the study area in the last 30 years shows a wave-like characteristic with an overall apparent upward trend. The vegetation cover in the study area is predominantly increasing and the spatial distribution shows a phased and regional character. Compared with 1990, there is a significant increase in the area of cultivated land in 2020. Among them, the areas of vegetation growth mainly occur in the basin around the Tarim River. Human activities have weakened the influence of natural factors on FVC. The results of the study suggest that the GEE platform can be an effective tool for permanently monitoring vegetation. desert oasis; vegetation coverage; Google Earth Engine; Hurst index; coefficient of variation; change detection +
Footnote †: journal: Applied Sciences  
MODIS image data, MODIS-related series data products or Landsat image data of certain periods are mostly used in the research of dynamic change in vegetation coverage, which are extracted and processed by MRT, ENVI and other software [7; 8; 9; 10; 11]. Google's newly developed Google Earth Engine (GEE) cloud platform combines massive petabyte-scale data acquisition, spatial visualization image processing and high-performance computing analysis. The platform stores over 200 public datasets, including Landsat, MODIS, Sentinel, ALOS and other series of satellite data, as well as CHIRPS and other meteorological products data, which can provide long-term, high-resolution satellite image data at the global scale. The powerful data processing capability greatly shortens the calculation time of satellite image data, improves the working efficiency and provides high accuracy and standardization for the dynamic monitoring of vegetation cover and it has been widely used in crop growth monitoring, land-use-type classification and other aspects [12]. Located in the south of Xinjiang, on the northern edge of the Taklamakan Desert, Alar is a typical man-made oasis in an arid region. Ecosystems are fragile and unstable, and climate change and human activities have led to a series of ecological problems, such as the expansion of desert areas, forest destruction, grassland degradation, river breakage, oasis degradation, etc. [13]. In recent decades, the state has attached great importance to ecological problems; a series of projects and policies have been launched since the 1950s to combat desertification and restore the ecology, and the results have been remarkable. During the ten years from 2010 to 2020, China has completed a total of 1.88 million square kilometers of desertification prevention and control tasks, and 0.177 million square kilometers of desertification land has been banned and protected. The area of desertification land nationwide has decreased by 432.67 square kilometers. The above data are from the State Forestry and Grassland Administration ([[http://www.forestry.gov.cn/](http://www.forestry.gov.cn/)]([http://www.forestry.gov.cn/](http://www.forestry.gov.cn/)), accessed on 17 June 2022). To study the spatial and temporal changes in vegetation in the region, it is important to obtain the precise vegetation conditions at different times in the study area, which is of scientific guidance to maintain the ecological balance and ecological environment restoration in the Tarim River basin and improve the local climate regulation capacity.