Quantitative Assessment of Urban Expansion Impact on Vegetation in the Lanzhou-Xining Urban Agglomeration  
[PERSON]  
1, [PERSON] [PERSON]  
and [PERSON] Liang  
School of Surveying and Land Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China; [EMAIL_ADDRESS] (W.W.J. ); [EMAIL_ADDRESS] (H.J. ); [EMAIL_ADDRESS] (J.Z. ); [EMAIL_ADDRESS] (K.Z. ); [EMAIL_ADDRESS] (Q.M. ); [EMAIL_ADDRESS] (S.Z. ); [EMAIL_ADDRESS] (X.L  
likely intensifies soil erosion in the surrounding areas, increasing the risk of landslides and other natural disasters [8; 9]. These problems are more serious in the fragile environments of arid regions. The Lanzhou-Xining (Lanxi) urban cluster in China is a classic arid region located in the western region of China; it serves as a crucial node in the \"Belt and Road Initiative\" and represents a typical arid region in China [10], therefore, the Lanxi region holds significant strategic importance. With the advancement of the \"Belt and Road Initiative\", the economic and population scales of the Lanxi area have further increased, leading to a notable rise in human activities and accelerating the pace of urban expansion. Due to the low precipitation and high evaporation rates, there is rapid moisture loss and low soil humidity in the Lanxi urban cluster. These environmental conditions are not conducive to forest growth. As a result, the Lanxi area is predominantly covered by grassland supporting livestock farming and ecological balance, while cropland is significant, and forest and shrubland occupy relatively small areas with low tree cover [11; 12]. Urban expansion negatively affects vegetation by directly occupying it [13; 14; 15], whereas urban greening and improved city management have positive effects on vegetation [16; 17]. However, there is still a lack of methods for accurately and quantitatively assessing both the positive and negative impacts of urban expansion on vegetation. Effectively assessing the impact of urban expansion on vegetation in arid areas is of paramount importance for promoting sustainable development in these urban regions [18; 19; 20]. Numerous studies have demonstrated that the impact of urbanization on arid regions can be quantified using various remote sensing indicators, such as the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) [21; 22; 23; 24; 25]. For example, [PERSON] et al. evaluated the impact of urbanization on vegetation cover in 117 major cities in China over the past three decades via the NDVI. The study revealed that urban expansion from 1982 to 2006 reduced vegetation greenness in arid regions of Northwest China, with a significant decrease in the average NDVI. While the NDVI is one of the most commonly used vegetation indices, its susceptibility to atmospheric and soil influences makes it more suitable for assessing vegetation in areas where atmospheric and soil conditions are relatively stable. [PERSON] et al. conducted improved research using the EVI and reported that urban expansion in arid lands of the southern United States from 2000 to 2020 led to a decrease in regional vegetation coverage [26]. Compared with the NDVI, the EVI is more resistant to atmospheric interference and is more capable of reflecting vegetation structure and chlorophyll content [27]. In the aforementioned study, they proposed the direct impact of water flux on vegetation, but the EVI cannot be used to differentiate the effects of precipitation. Compared with the NDVI and EVI, the net primary productivity (NPP) has the advantage of directly reflecting vegetation productivity and the ability to monitor changes in vegetation productivity over the long term [28]. [PERSON] et al. investigated the influence of urban expansion on arid land vegetation in China through NPP and reported a correlation between the growth of urban land area and the loss of vegetation NPP from 2000 to 2006 [29]. However, there is a clear correlation between NPP and precipitation, where NPP decreases with decreasing precipitation.