## 3 Results
### Sensitivity Analysis of Vegetation to Different Types of Drought Stress  
After analyzing the spatial distribution of correlation coefficients and significance levels between NDVI and SPEI by one month, six months, and across different seasons and years from 2000 to 2018 in the West Liao River Basin, the results are shown in Figures 6 and 7. Figure 6 shows that at the 1-month time scale (Figure 6a,a'), the correlation coefficients between NDVI and SPEI ranged from \(-0.32\) to \(0.12\). Western regions exhibit more negative correlations than other areas. Strong significant negative correlations (\(p<0.05\)) dominated in some parts of western, central, southern, and eastern areas, while weak positive correlations appeared in some northern areas. At the 6-month time scale (Figure 6b,b'), correlation coefficients varied from \(-0.40\) to \(0.34\). Positive correlations prevailed in most areas, except for negative correlations in the western and central regions. Significance testing revealed weak positive/negative correlations across most of the basin, with only small areas in the northwestern part showing strong positive correlations. The correlation coefficients between NDVI and one-year-lagged SPEI spanned \(-0.72\) to \(0.85\) (Figure 6c,c'). Negative correlations dominated most areas, though positive correlations appeared in some areas of the eastern and central regions. Most areas showed weak negative/positive correlations, with exceptions in eastern regions (strong/very strong significant positive correlations) and southern regions (strong significant negative correlations). Figure 7 shows that in spring, the correlation coefficients ranged from \(-0.81\) to \(0.84\). Most areas exhibited positive correlations, with about \(16\%\) showing highly significant or significant positive correlations, primarily in the central regions. Conversely, the western regions displayed more negative correlations, particularly in the west, south, and north. During summer, correlation coefficients ranged from \(-0.62\) to \(0.91\). Approximately \(98\%\) of the area showed positive correlations, with \(43\%\) being highly significant. Negative correlations were observed in some western and central areas but were relatively minor. In autumn, correlation coefficients ranged from \(-0.74\) to \(0.79\). Most regions exhibited insignificant positive correlations, with only about \(8\%\) in the east showing significant or highly significant positive correlations. Some northern and central areas displayed insignificant negative correlations. Winter correlation coefficients ranged from \(-0.80\) to \(0.63\). About \(98\%\) of the area showed negative correlations, with \(37\%\) in the east, south, and west exhibiting significant or highly significant negative correlations. Only a few northern and central areas showed insignificant positive correlations. On an annual scale, correlation coefficients ranged from \(-0.61\) to \(0.87\). Overall, \(81.9\%\) of the basin exhibited positive correlations, with about \(20.8\%\) of the basin mostly distributed in the east showing significant positive correlations. The northwestern regions mainly displayed insignificant negative correlations. In summary, the correlation between NDVI and SPEI in the West Liao River Basin exhibits significant spatial heterogeneity across seasons and years. Positive correlations dominate in spring and summer, especially in summer, while autumn shows  
widespread but less significant positive correlations. Winter is predominantly characterized by significant negative correlations. On an annual scale, positive correlations prevail, with significant positive correlations concentrated in the east-central region and insignificant negative correlations in the northwestern region. These results indicate that the vegetation response to drought in the West Liao River Basin varies significantly by month, season, and region.