## 3 Results  
### Characteristics of NDVI Distribution and Change  
The analysis of the average NDVI from 2000 to 2020 in the Aksu region reveals significant spatial heterogeneity in vegetation coverage (Figure 3). Vegetation is primarily concentrated in Aral City and Aksu City, where the average NDVI reaches 0.48. Following these are Baicheng County, Wensu County, Awati County, Wushi County, and Kuqa County, with an average NDVI of approximately 0.4. The lowest is in Shaya County, where the average NDVI is only 0.23, mainly due to the presence of desert and bare land in the southern part of the county, resulting in low vegetation coverage.  
Based on trend analysis and slope changes, NDVI trends were categorized into five classes (as shown in Figure 4). The phase-wise analysis is described below.  
From 2000 to 2005, a significant increase in NDVI was observed, with 65% of the area showing an increasing trend and 30% showing a decreasing trend.  
Between 2006 and 2010, the increasing trend accounted for 62% of the area, while the decreasing trend accounted for 34%, indicating a continued rise in NDVI during this period.  
\begin{table}
\begin{tabular}{c c c} \hline
**Category** & **Condition** & **Description** \\ \hline Significant Decrease & a \textless{} 0 and \(p\leq 0.01\) & NDVI shows a significant decreasing trend (high significance level, \(p\leq 0.01\)). \\  & a \textless{} 0 and & NDVI shows a decreasing trend with moderate significance (0.01 \textless{} \(p\leq 0.05\)). \\  & 0.01 \textless{} \(p\leq 0.05\) & NDVI change is not significant, with no clear trend observed. \\   No Significant Change & \(p\textgreater{} 0.05\) & Trend observed. \\  & a \textgreater{} 0 and & NDVI shows an increasing trend with moderate significance (0.01 \textless{} \(p\leq 0.05\)). \\   Moderate Increase & \(0.01\textless{} \(p\leq 0.05\) & NDVI shows a significant increasing trend (high significance level, \(p\leq 0.01\)). \\   Significant Increase & a \textgreater{} 0 and \(p\leq 0.01\) & NDVI shows a significant increasing trend (high significance level, \(p\leq 0.01\)). \\ \hline \end{tabular}
\end{table}
Table 2: Classification of change trends.  
From 2011 to 2015, the decreasing trend (50%) exceeded the increasing trend (44%), indicating a decline in vegetation coverage.  
Between 2016 and 2020, NDVI rebounded, with the increasing trend covering 57% of the area and the decreasing trend covering 38%.  
Overall, from 2000 to 2020, NDVI in Aksu showed a significant increasing trend, with 85% of the area experiencing an increase and only 9% showing a decreasing trend, suggesting an improvement in regional vegetation coverage.  
The analysis indicates that vegetation coverage in Aksu experienced varying degrees of fluctuation across different phases, particularly with a downward trend between 2011 and 2015, followed by a recovery from 2016 to 2020. These findings align with the economic development, urban expansion, and ecological engineering projects implemented in different counties of Aksu, providing insights into vegetation change in the region.  
Figure 4: NDVI change trends in Aksu from 2000 to 2020.  
Figure 3: Spatial distribution map of average NDVI in the Aksu region from 2000 to 2020.  
The interannual variation of NDVI in Aksu from 2000 to 2020 is shown in Figure 5. During this period, NDVI displayed a significant increasing trend, with an annual growth rate of 0.83% (\(p<0.05\)). The growth rate peaked between 2010 and 2012 at 3.05% per year (\(p<0.05\)), while a slight decline was observed from 2018 to 2020 at 0.33% per year (\(p<0.05\)). Overall, the trend indicates a notable improvement in vegetation coverage in Aksu over the study period.