## 3 Results
### Temporal Variation Trends of SPEI  
Figure 4 and Table 3 depict the interannual and seasonal variations of SPEI from 2000 to 2018, along with results from Sen's trend analysis and Mann-Kendall tests. Overall, SPEI exhibited a fluctuating upward trend, though not statistically significant, with a Sen slope of 0.02742/year. Annual SPEI values ranged from \(-\)0.94 (2002, the driest year) to 0.62 (2012, the wettest year) (Figure 4e).  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Annual** & **Spring** & **Summer** & **Autumn** & **Winter** \\ \hline Sen slope (/a) & 0.00179 & 0.00998 * & 0.00420 * & 0.00208 * & 0.00022 \\ MK test & 1.69969 & 2.09913 & 2.51896 & 2.02916 & 0.34985 \\ \hline \end{tabular} Note: * means that it passed the significance level test of 0.05.  
\end{table}
Table 2: Significance level of annual and seasonal NDVI variations for vegetation.  
Figure 3: Spatial distribution of annual and seasonal NDVI variations for vegetation. Note: (**a**) spatial distribution of spring NDVI variations for vegetation according to slope; (**a**) spatial  
distribution of spring NDVI variations for vegetation according to significance; (**b**) spatial distribution of summer NDVI variations for vegetation according to slope; (**b\({}^{\prime}\)**) spatial distribution of summer NDVI variations for vegetation according to significance; (**c**) spatial distribution of autumn NDVI variations for vegetation according to slope; (**c\({}^{\prime}\)**) spatial distribution of autumn NDVI variations for vegetation according to slope; (**c\({}^{\prime}\)**) spatial distribution of autumn NDVI variations for vegetation according to significance; (**d\({}^{\prime}\)**) spatial distribution of winter NDVI variations for vegetation according to slope; (**d\({}^{\prime}\)**) spatial distribution of winter NDVI variations for vegetation according to significance; (**e\({}^{\prime}\)**) spatial distribution of annual NDVI variations for vegetation according to slope; (**e\({}^{\prime}\)**) spatial distribution of annual NDVI variations for vegetation according to significance.  
Seasonally, spring, summer, and autumn SPEIs showed fluctuating wetting trends, with autumn being significant. Winter exhibited a drying trend, though insignificant. Sen slopes were 0.01344 (spring, Figure 4a), 0.04575 (summer, Figure 4b), 0.07995 (autumn, Figure 4c), and \(-\)0.00591 (winter, Figure 4d) per year. Specific ranges and extreme years varied by season, highlighting distinct seasonal wet-dry dynamics. Mann-Kendall tests revealed multiple intersection points within confidence intervals, indicating significant trend shifts across seasons and years. Notably, spring SPEI shifted negatively in 2002, then positively after 2005 (Figure 4a'). Summer trends showed a significant wetting shift around 2001 (Figure 4b'). Autumn exhibited wetting shifts in multiple years post-2003 (Figure 4c'). Winter transitioned from drying to wetting post-2011 (Figure 4d'). The annual SPEI showed a significant wetting shift in 2004 (Figure 4e').  
In summary, the West Liao River Basin\({}^{\prime}\)s SPEI displayed a fluctuating upward trend from 2000 to 2018, though not statistically significant. Seasonal wet-dry variations were pronounced, reflecting the complexity and seasonality of climatic changes in the region.