## 3 Results
### Response of Vegetation to Drought in Xinjiang
#### 3.3.2 Spatial Distribution of Vegetation Condition Response Times to Climate Change in Xinjiang  
The response times of vegetation conditions to climate change (different SPEI timescales) exhibited significant spatial variation in Xinjiang (Figure 12). The shorter the timescale corresponding to the highest correlation coefficient between the vegetation indices and SPEI, the faster the vegetation response to drought stress. Conversely, a longer timescale indicates a slower response, suggesting stronger drought tolerance. For NDVI, 54.4% of the region showed a strong correlation with SPEI03, representing the broadest spatial distribution across the study area, which was primarily concentrated in southwestern Xinjiang. Only 0.6% of the region responded strongly to the mid-term climate change. In 21.3% of the area, the NDVI was significantly correlated with SPEI12, mainly in northern  
Figure 11: Maximum correlation coefficients between vegetation indices and SPEI. Box plots depict the distribution of maximum correlation coefficients (R\({}_{\text{max}}\)) between NDVI and SIF with SPEI, separated by ecological regions (R1–R5) and vegetation types (Forest, HCG, MCG, and LCG). (**a**) shows NDVI correlations across ecological regions, whereas (**b**) displays SIF correlations. (**c,d**) present NDVI and SIF correlations, respectively, by vegetation type. Xinjiang and the western Iii region (ecological regions R1, R2, and R3). Additionally, 23.7% of the region showed a strong correlation between NDVI and SPEI24, primarily in the eastern areas. This indicates that the vegetation in Xinjiang is influenced by both short- and long-term climate change. The timescale distribution of the SIF response to SPEI revealed that 39.1% of the region exhibited a strong correlation with SPEI12. According to the available SIF data, vegetation in northern Xinjiang is mainly affected by long-term climate change, which is closely aligned with the pattern observed for NDVI. Figures 10 and 12 complement each other by providing spatial and temporal perspectives on vegetation responses to drought. Figure 10 emphasizes spatial sensitivity, while Figure 12 highlights temporal dynamics, offering a more comprehensive understanding. The timescale of vegetation response to climate change varies significantly across different ecological regions and vegetation types (Figure 13). Based on NDVI analysis, the response times of vegetation growth to climate change were similar in the R3, R4, and R5 ecological zones. In R3, the largest proportion of the NDVI response was to SPEI03 (69.8%), whereas R4 and R5 exhibited greater response areas to SPEI24 than R3, accounting for 31.3% and 36.0%, respectively. For all five ecological zones, the proportion of NDVI responses to SPEI12 decreased sequentially, with the highest percentages occurring in R1 and R2 (67.0% and 63.1%, respectively). This suggests that vegetation in the R1 and R2 regions of northern Xinjiang exhibited the highest drought tolerance, followed by southern R4 and R5 regions, with central R3 displaying the lowest tolerance. Among the vegetation types, low-coverage natural grasslands had the longest response times to climate change, with the largest proportion of NDVI responses associated with SPEI24 (18.63%). Natural forests showed the smallest response to SPEI24; however, they had a high response to SPEI12, covering 65.2% of the area. For natural grasslands, the lower the coverage, the greater the proportion of the NDVI response to SPEI03, whereas the response to SPEI12 was smaller. This indicated that as grassland coverage decreased, drought tolerance weakened. A contrasting trend was observed between the SPEI24 and SPEI12 response proportions, indicating that prolonged interannual climate change adversely affected low-coverage grasslands.