## 3 Results
### Spatiotemporal Distribution of Vegetation Growth in the Mining Area
#### 3.1.2 Temporal Distribution Characteristics of Vegetation Growth  
Figure 10 shows the seasonal variation of kNDVI values in the Huojituo mining area from 1999 to 2023. In winter, due to the cold and dry climate conditions, vegetation withers, and the kNDVI value drops to its lowest point. At this time, vegetation is almost completely in a dormant state. In spring, as temperature rises and precipitation increases, vegetation begins to enter the growing season, and the kNDVI value gradually increases, reflecting the process of vegetation gradually recovering from its winter dormant state. In summer, vegetation enters the peak growth period, and the kNDVI value reaches its highest point of the year, indicating that plant photosynthesis is active, and biomass is increasing. In autumn, temperature drops, and vegetation gradually enters the dormant period, and  
Figure 8: Spatial distribution of changes in NDVI and kNDVI from 1999 to 2023.  
Figure 9: Remote sensing image data acquired in the study area: (**a**) RGB Orthophoto Map, (**b**) kNDVI, and (**c**) NDVI.  
the kNDVI value begins to decline. This stage reflects the decline in vegetation coverage and the weakening of plant physiological activities. Therefore, the results show a clear phenological cycle change in the mining area, with the vegetation growing season mainly being in the summer. The slope of the trend line of the highest kNDVI point is 0.00132, with an R\({}^{2}\) value of 0.592; the slope of the trend line of the lowest kNDVI point is 0.00029, with an R\({}^{2}\) value of 0.697, indicating that both the vegetation growing season and non-growing season kNDVI values increase, and the kNDVI change in the growing season is more significant.  
Using the MK mutation test method, we identified two abrupt change points in the long-term vegetation growth trend of the mining area, occurring in 2011 and 2018 (Figure 11a). These change points fall within the \(\pm\)1.96 confidence interval at the 0.05 significance level, indicating that they are statistically significant mutation points in the vegetation growth trend. Consequently, the vegetation growth was divided into three distinct phases based on the time series: 1999-2011, 2011-2018, and 2018-2023. According to the annual changes in kNDVI during the vegetation growth period (Figure 11b), in the first phase (1999-2011), the range of kNDVI changes was relatively small, characterized by a gradual upward trend with fluctuations. The annual average kNDVI value increased from 0.039 to 0.083 at an annual growth rate of 0.0037/a. In the second phase (2011-2018), kNDVI exhibited significant variability, with its annual average value fluctuating between 0.083 and 0.218, maintaining an annual growth rate of 0.0193/a. In the third phase (2018-2023), kNDVI showed substantial variation, with its annual average value decreasing from 0.218 to 0.127, indicating a rapid decline at an annual rate of 0.0182/a.  
Figure 11: Time variation of kNDVI in the Huojitu mining area from 1999 to 2023: (**a**) MK mutation test, and (**b**) interannual variation.  
Figure 10: kNDVI seasonal changes in the Huojitu mining area from 1999 to 2023.