## 3 Research Area  
The Ministry of Ecology and Environment of the People's Republic of China identified eight ecologically fragile areas in China with the ecotone as the main body (Ministry of Environmental Protection, 2008): 1. Northeast forest grass ecotone; 2. northern agriculture pasture ecotone; 3. northwest desert oasis ecotone; 4. southern red soil hilly mountain ecotone; 5. southwestern karst mountain rocky desert ecotone; 6. southwestern mountain farming and pasture ecotone; 7. Qinghai-Tibet Plateau complex-erosion, ecologically fragile zone; 8. coastal water-land junction zone. With the deepening of Earth system science and sustainable development research, the existing ecologically fragile zoning has not adapted to the needs of the new situation. The comprehensive ecological division that integrates natural elements and social and economic factors is currently the main trend and the principle of  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(n\) & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** \\ \hline \(RI\) & 0.00 & 0.00 & 0.58 & 0.90 & 1.12 & 1.24 & 1.32 & 1.41 & 1.45 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Average random consistency indicator \(RI\).  
dividing the research area in this study. To identify ecologically vulnerable areas, carbon flux was used to divide the study area.  
Net primary productivity (NPP) is the total amount of organic dry matter that can be produced by green plants per unit time and unit area. This value reflects the ability of plants to utilize natural environmental resources and is a key link in the biogeochemical carbon cycle. The temporal and spatial variations in NPP are mainly determined by the complex interactions between vegetation, soil, and climate, and they are strongly influenced by human activities and global environmental changes [34]. Human disturbances, especially those associated with land use change, have equal or even more severe ecosystem productivity than those physiological changes associated with climate composition [35]. If the resilience and adaptability of ecosystems are severely damaged, these ecosystems may be at risk. The increase in global warming will lead to increased risks to the ecosystems in the 21 st century. In turn, feedback from global carbon that sinks to atmospheric carbon dioxide pools can accelerate or limit climate change [36]. The estimation process of NPP is as follows [37]:  
\[GPP=\sum A\ dt \tag{1}\]  
and  
\[NPP=GPP-Ra \tag{2}\]  
where gross primary production (\(GPP\)) is the cumulative sum of \(A\) at every time step (\(dt;s\)); \(A\) represents the parameterizations for leaf photosynthesis [38]; and Ra is the autotrophic respiration [39], determined by temperature and tissue nitrogen content.  
To reflect the changes in the patterns of vulnerable eco-regions in the future, this study selected the NPP data from the MPI-ESM-LR(Max Planck Institute Earth System Model) model from 2021 to 2050 as a typical period to represent the medium-term trend (based on 1988-2017) (Figure 1). The MPI-ESM-LR includes a detailed spatial separation rate and considers complex human activities that reflect the ecological issues we care about, and the modular land surface scheme (Jena Scheme for Biosphere-Atmosphere Coupling in Hamburg) brings simulation results closer to real values [40]. Under the low-emissions scenario (RCP 4.5), vulnerable eco-regions are expected to be concentrated in the southern region. For the high-emissions scenario (RCP 8.5), the area may extend north to the central and northeastern regions. It is worth noting that regardless of the type of emissions scenario, the ecosystem of the western region will develop, at least until 2050, while the region from south to southwest will become a new ecologically fragile zone. This change may be mainly due to increased drought in Southern China [41]. Therefore, in this study, the traditional arid zone was combined with the new vulnerable eco-region as a drought risk assessment research area.