# Vegetation Dynamics and Recovery Potential in Arid and Semi-Arid Northwest China
## 2 Results
### Response of Vegetation Restoration Potential to Climate Warming and Humidification  
Based on historical temperature and precipitation data collected from meteorological stations between 1961 and 2020, the spatial analysis results for northwest China are as follows: the temperature distribution exhibited a distinct westward-high, eastward-low pattern, as well as a northward-high, southward-low trend. Areas characterized by the highest temperatures were primarily concentrated in expansive regions encompassing central Xinjiang, southeastern Gansu, Ningxia, and western Inner Mongolia. In contrast, lower temperatures prevailed in the southern parts of Xinjiang, extensive areas of Qinghai, and northeastern Inner Mongolia. Notably, the temperature variability across the study area exhibited considerable spatial heterogeneity (Figure 8). Regarding precipitation, the overall distribution showcased elevated levels in the northwestern and southeastern fringes of the region, juxtaposed with a marked precipitation deficit in the central expanse. Regions with heightened precipitation were chiefly clustered in the northwestern sector of Xinjiang, Qinghai, the southern part of Gansu, and the eastern and northern sectors of Inner Mongolia. Conversely, areas with diminished precipitation were predominantly situated in the central portion of Xinjiang, as well as border regions shared with other provinces (Figure 8). Studies have shown that precipitation is the primary factor affecting vegetation in northwest China, and based on this, it is necessary to analyze the aridity index (SPEI) in northwest China. The SPEI, a drought index, exhibits notable variations in volatility across different time scales. These variations in the time-scale length and frequency of fluctuations  
Figure 8: Spatial distribution of station-measured annual mean temperature (**a**) and precipitation (**b**) in northwest China during 1961 to 2019. Figure 7: Differences in vegetation restoration potential index between LPJ-simulated maximum recovery cover and satellite-observed current vegetation cover in northwest China from 1982 to 2019.  
display a consistent pattern, highlighting the strong stability of longer time scales. In this study, the SPEI-12 index was chosen to illustrate the evolving climate trends of warming and humidification in northwest China from 1961 to 2019 (Figure 9). It can be observed that northwest China experienced a higher frequency of drought events during the periods of 1961-1986 and 1997-2011. Conversely, during the periods of 1986-1997 and 2011-2019, the occurrence of humid events became more prevalent, indicating an overall shift from dry to wet conditions. Therefore, in conjunction with the increasing temperature trend, it becomes evident that the climate in northwest China has undergone a significant pattern of warming and humidification. Precipitation is the most important natural factor limiting vegetation growth in the study area [35]. To investigate the response of vegetation conditions to drought conditions, the spatial correlation and significance of the multi-year mean values of the NDVI and SPEI-12 from 1982 to 2019 were analyzed. As shown in Figure 10a, the response of annual vegetation growth to the annual-scale drought index SPEI-12 was high, with a maximum correlation coefficient of 0.73, a minimum correlation coefficient of \(-0.71\), and a mean correlation coefficient of 0.06. Higher correlation coefficients were mainly distributed in central Inner Mongolia, northwestern Xinjiang, Qinghai, and northern Gansu, and lower correlation coefficients were mainly distributed in western Inner Mongolia, southwestern Xinjiang, northern Qinghai, and northern Gansu. As shown in Figure 10b and Table 5, the annual NDVI and the annual-scale SPEI-12 in most of the regions showed a non-significant correlation, accounting for 81.08%, with the positive correlation being more non-significant than the negative correlation.