# Vegetation Dynamics and Recovery Potential in Arid and Semi-Arid Northwest China
## 2 Results  
### Climate-Driven Vegetation Dynamics in Northwest China  
This section utilizes NDVI data from AVHRR remote sensing imagery and NDVI data from LPJ simulations for vegetation greening analysis in the northwest. From 1982 to 2019, the regional average NDVI in northwest China showed a significant increasing trend (Figure 1b). The highest NDVI value was recorded in 2018 (0.38), and the lowest in 1989 (0.29). Spatially, vegetation coverage in northwest China was generally low (Figure 1a), with most areas characterized by sparse vegetation (NDVI! 0.4). These areas, accounting for 63.6% of the study region, were dominated by unused land types such as deserts and partially degraded grasslands. Regions with NDVI values between 0.4 and 0.6 were mainly located in central Qinghai, Gansu, Inner Mongolia, and Ningxia, as well as northwestern and central Xinjiang. These areas, covering 20.2% of the study region, were primarily cropland and some grasslands. Areas with high vegetation coverage (NDVI! 0.6) were found in northeastern Inner Mongolia, southeastern Qinghai, southern Gansu, and northwestern Xinjiang, where forests and grasslands were predominant, accounting for 16.2% of the region. According to LPJ model simulations, the regional average NDVI in northwest China also showed a significant increasing trend from 1982 to 2019, with the highest value in 2019 and the lowest in 2001 (Figure 1d). Regarding the spatial distribution of the grassland NDVI, the LPJ-simulated NDVI displayed spatial heterogeneity (Figure 1c), with higher NDVI values in the northeast, northwest, and southeast and lower values in the central region. Low NDVI values were concentrated around deserts, while high values were observed in the Tianshan Mountains, Daxinganling Mountains in Inner Mongolia, and Qinling Mountains. From 1982 to 2019, 33.82% of the total area in northwest China experienced a significant increase in the NDVI, 6.08% showed a moderate increase, and 2.8% displayed a slight increase (Figure 2a, Table 1). Figure 2c shows that during 1982-2000, NDVI trends were not significant, with only 20.63% of the regions exhibiting an increasing trend, and 78.36% showing no significant change. However, between 2001 and 2019, areas with a decreasing NDVI expanded to 24.13%, while areas with an increasing NDVI accounted for 16.18%, indicating simultaneous vegetation restoration and degradation after 2000 (Figure 2e). Areas with an increasing NDVI from 1982 to 2019 were mainly located in eastern and southern Inner Mongolia, Ningxia, southern Gansu, eastern and western Qinghai, and northern and western Xinjiang. In contrast, southern Xinjiang, northern Qinghai, northern Gansu, and western Inner Mongolia showed a declining trend, with 21.3% of the regions experiencing a significant decrease in the NDVI. The LPJ simulation results showed that from 1982 to 2019, 52.39% of the total area in northwest China had a significant increase in the NDVI, 5.63% showed a moderate increase, and 3.04% displayed a slight increase (Figure 2b, Table 2). Figure 2d indicates that during 1982-2000, NDVI trends were not significant, with only 40.81% of the regions exhibiting an increasing trend, while 54.4% showed no significant change. However, between 2001 and 2019, areas with a decreasing NDVI accounted for 0.62%, while areas with an increasing NDVI accounted for 62.72%, indicating substantial vegetation recovery after 2000 (Figure 2f). Areas with an increasing NDVI from 1982 to 2019 were primarily located in eastern and western Qinghai and northern and western Xinjiang. In contrast, eastern Inner Mongolia showed a declining trend, with 0.2% of the regions experiencing a significant decrease in the NDVI.