## 5 Discussion
### Transition of Vegetation Vulnerability under Different Scenarios in the MRB  
The stochastic matrix was used to quantitatively analyze the transition of vegetation vulnerability of different periods in the MRB. To our knowledge, it is the first time that the stochastic matrix has been used in vegetation vulnerability research. A stochastic matrix was chosen because it can reflect the transition simply and directly [41].  
Under SSP1-2.6, the impact of human factors on vegetation vulnerability in MRB decreased and was less than the impact of natural factors. The climate will become warmer and wetter, making it more suitable for vegetation growth under the SSP1-2.6 [42], and the vegetation vulnerability will be the lowest [43]. Therefore, the vegetation vulnerability in the MRB increased a little from the base period to the near future period but slightly decreased from the near future period to the distinct future period.  
Under SSP2-4.5, the impact of natural and human factors on vegetation vulnerability for the near future period was similar to the factors impact for the base period, but the impact of human factors on vegetation vulnerability for the distinct future period increased by 14% compared to the base period in the MRB. Under the SSP2-4.5 scenario, moderate warming would lead to a slight drought [44], and underdeveloped countries will face pressure from low education, high population growth, and intensified land use, including reduced forest and grassland [14]. For the MRB which is a low-developed area, the conflict environment of reduced vegetation, increased population, and regional competitions will make the increasing vegetation vulnerability.  
Under the SSP5-8.5, the impact of human factors on vulnerability was 1.4 times greater than natural factors for the distinct future period. The vegetation vulnerability in the distinct future period increased by 950.00% compared to the base period, which was the highest vulnerability increase under all scenario assumptions. Under the SSP5-8.5 scenario, the population at risk of drought is projected to increase by 45.40% in the 2050s, this will increase vulnerability in 80% of global land areas [45], resulting in severe vegetation damage. For the MRB, which relies on agriculture and tourism to develop, increased vegetation vulnerability and damaged vegetation severely can seriously hinder further economic development.  
The transition of vegetation vulnerability varied greatly under different scenarios. Under the sustainable SSP1-2.6, the increase in vegetation vulnerability was the smallest from the base period to the near future period, and to the distinct future period, the long-term vulnerability was 1.83 times that of the base period. Under SSP5-8.5, vegetation vulnerability increased the most from the base period to the near future period and to the distinct future period, the long-term vulnerability was 9.5 times that of the base period.  
Therefore, sustainable development is of great significance for vegetation protection [46]. In the MRB, where vegetation has been damaged due to socio-economic development, taking a low-emission development is an effective method to protect the vegetation environment.  
However, there are still some limitations. When constructing a vegetation vulnerability assessment system, more consideration was given to natural factors, and fewer indexes were selected for human factors. In addition, the direct and indirect effects of human and natural factors on vegetation vulnerability were not comprehensively considered, which increased the uncertainty of the results. In future research, it is necessary to search for suitable datasets and establish a more comprehensive assessment system by using more comprehensive methods.