# Monitoring Vegetation Change and Its Potential Drivers in Inner Mongolia from 2000 to 2019
## 3 Results
### Future NDVI Trends  
In this study, the Hurst index values for annual NDVI data were calculated on a pixel-by-pixel basis using MATLAB (Figure 8a). The Hurst index of NDVI in Inner Mongolia is low, with maximum, minimum, and mean values of 0.93, 0.09 and 0.44, respectively. The proportion of areas with a Hurst index less than 0.5 was 74.91%, while that of areas greater than 0.5 was 25.08%, indicating that the reversal of the vegetation trend in the future is likely in most areas of Inner Mongolia. This indicates that future changes will be the opposite to those in the present. Furthermore, the Hurst values are low in the border areas  
Figure 7: Spatial distributions of trends before and after mutation in Inner Mongolia during 2000–2019. (**a**) trends of NDVI before mutation, (**b**) trends of NDVI after mutation.  
between Inner Mongolia and Mongolia and relatively high in other areas. Additionally, the areas with a Hurst index greater than 0.5 are concentrated in the south of Chifeng, Xilingol League, and Alxa League.  
The Sen's slope and Mann-Kendall test can gradually quantify trends in the NDVI, and the Hurst index can be used to qualitatively predict whether future trends will be similar to those at present. However, neither of these methods can predict future increases or decreases in trends. The NDVI trends were coupled with the Hurst index classification results to obtain the spatial distribution of future changes of vegetation cover in Inner Mongolia (Figure 8b), and the future change trends were classified into the following four levels: \"increased,\" \"constant,\" \"decreased,\" and \"unable to determine,\" which were used to provide reasonable predictions of future vegetation change trends. Where \"increased\" and \"decreased\" represent predicted increases and decreases in future NDVI trends passing the 0.05 significance level in the Mann-Kendall test, respectively. The remaining NDVI trends that did not pass the 0.05 significance level, as well as the areas that were unchanged were notes as constant. The results showed that the area with stable and constant NDVI was the largest. Areas with increased NDVI in Inner Mongolia are larger than areas with decreased NDVI. Increased areas account for approximately 24.62% of the total area and are mainly located in Hulunbeier, Xing'an League, eastern Tongliao, and south-central Alxa League, which may be due to the large-scale ecological management and soil and water conservation and afforestation policies in these areas. Meanwhile, decreased areas, which account for about 10.56% of the total area of Inner Mongolia, are concentrated in the southern part of Inner Mongolia, which is mainly arable land and highly influenced by human activities. In addition, the Wuliang Suhai area in Bayannur, located in the lower reaches of the Yellow River, has experienced vegetation degradation due to increasing ecological pollution [72]. The areas with stable and constant future trends of NDVI accounted for 64.81% of the total area and were distributed throughout the region. In the areas with stable and constant NDVI levels, areas with positive Sen's slope values and \(p>0.05\) are the largest. This indicates that areas with increasing NDVI in Inner Mongolia will increase more areas with decreasing NDVI in the future.  
Figure 8: Spatial distribution of the Hurst index and future NDVI trend levels in Inner Mongolia during 2000–2019. (**a**) Hurst index, (**b**) Future NDVI trend levels.