**1. Introduction**

An oasis is a small-to-medium-scale landscape maintained by a water supply in an arid or semi-arid desert area [1]. It is also an unstable ecosystem, with the characteristic of high habitat fragmentation. In China, oases are mainly distributed in arid and semi-arid regions to the west of the Helan Mountians, whose area is only 5% of the total. They support the survival of 90% of people and the economic development of 95% [2]. Therefore, changes in the ecosystem of oases can have a considerable influence on both ecological security and sustainable socioeconomic development [3].

The Hexi Corridor in northwestern China, which is a region affected by human activities, climate change, and tectonic activities [4], is one of the most important, but

**Citation:** Jiang, Y.; Du, W.; Chen, J.; Wang, C.; Wang, J.; Sun, W.; Chai, X.; Ma, L.; Xu, Z. Climatic and Topographical Effects on the Spatiotemporal Variations of Vegetation in Hexi Corridor, Northwestern China. *Diversity* **2022**, *14*, 370. https://doi.org/10.3390/ d14050370

Academic Editor: Michael Wink

Received: 18 April 2022 Accepted: 5 May 2022 Published: 6 May 2022

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vulnerable, oasis ecosystems in the arid and semi-arid regions of China [5] It has been reported that the dynamic changing of the oasis area in the Hexi Corridor is closely related to agricultural industry [6]. Moreover, combining vegetation and soil-related endmembers time series data can enhance conventional LUCC analysis, to help fully capture land degradation processes [7]. There is strong negative correlation between the water resource reserves and the NDVI of the area [8]. In particular, the evolution of an artificial oasis is closely correlated with human economic activities and the environmental carrying capacity of oases [9]. Natural factors and human activity controlled the desertification process, but the reversal of desertification mainly resulted from human activities [10]. In respect to oases, the socioeconomic development and ecological/environmental coordination among the different administrative regions within the Hexi Corridor vary greatly [11]. The expansion of cultivated land and unreasonable utilization of groundwater are the main factors associated with the climatic and environmental degradation of the Hexi Corridor [12]. The rapid process of urbanization and coordinated urban–rural development have reduced the ecosystem services of the Hexi Corridor [13]. Remote sensing is an effective way to extract spatial information, to monitor spatiotemporal variation at a regional scale. Of which, land-use maps can describe information about land surface coverage. Thus, this has been mostly used to analyze vegetation change. However, there is still a need for further investigation of both natural and human influences, especially in relation to long-term input data. In addition, the more detailed changes at local level need to be strengthened [14]. Investigation of the ecologic and environmental problems in the Hexi Corridor, which highlight the importance of natural and human activities as the driving forces of oasis change, could help boost the sustainable socioeconomic development of the region.

In this study, Landsat5/TM, Landsat8/OLI, MOD13A3, and PANDA data were used in combination with regional meteorological observations, to discuss the influence of climate change and human activities on oasis vegetation in the Hexi Corridor. The changes in the vegetation of the Hexi Corridor and areas of land use in the fluctuating regions were quantitated. In addition, DEM, population number, livestock number, settlement number, and GDP were collected to analyze their influence on oasis change. The findings of this work improve the understanding of the change mechanisms affecting oasis landscapes and provide a scientific basis to support policy makers.
