Abstract: Climate change and its effects on vegetation in the arid areas of northwest China have been a major con? cern in the geosciences community. The case study area, the Turpan Basin, is an area of approximately 5.85 × 10⁴ km² in the eastern part of Xinjiang Province in northwest China. The Turpan Basin’s topography consists of a low flat area in the center with high mountains surrounding it, yielding a large elevation difference in a small distance. Water vapor brought by prevailing westerly winds is the main source of moisture in this area. The basin’s climate is very dry and hot and the hydrothermal combination is complicated. In this paper, ground-based meteorological ob? servation data, GLDAS-2.1 reanalysis meteorological data, and satellite-based MODIS normalized difference vege? tation index (NDVI) data are used to investigate the impacts of climate change, terrain, and human activities on spa? tiotemporal changes of vegetation in the Turpan Basin from 2001 to 2017. The analysis uses the methods of trend test, linear regression, and partial correlation analysis. The results of this analysis indicate that the following. (1) There was no significant change in precipitation in the Turpan Basin overall; however, the rate of increase in the northern mountains is large. Additionally, the temperature increased significantly over the whole region, especially in the central area at the bottom of Turpan Basin, with a remarkable growth rate. (2) The NDVI of the whole region exhibited a very significant upward trend, and the NDVI growth rates in the mountains and the central region were relatively large. (3) Affected by the availability of water vapor and sunlight duration, the NDVI value is the highest in the mountains around the Turpan Basin at an elevation of approximately 3,000 m. In the northern Tianshan Moun? tains, which extend from east to west, and the combination of water and heat conditions is the best in the northwest- facing slopes, which is beneficial to vegetation growth. In contrast, the north-facing and south-facing slopes have ei? ther too little or too much solar radiation. In the western Tianshan Mountains, which generally extend generally south to north, the northwest-facing slopes also have the best combination of water and heat, whereas the southeast- facing slopes have the smallest NDVI. (4) Because of the special terrain, the hydrothermal combination in the Tur? pan Basin is complex. Although water is the major limiting factor for vegetation growth in most regions, as indicated by the positive correlation between precipitation and NDVI, the effects of temperature change on NDVI are compli? cated. In the mountains and desert areas, temperature is generally negatively related to NDVI, but in the central ar? ea at the bottom of the Turpan Basin, the relationship is positive because of the accumulation of groundwater from the surrounding mountains which provides a comparatively stable water supply.

Key words: Hydrothermal Combination, Vegetation Change, Climate Change, NDVI, Terrain, MODIS