## 4 Discussion
### Temporal Stability of ECIs and Their Impacts on Ecosystem at the Annual Scale  
A comprehensive assessment reveals that the ECIs significantly influence SWC, with FD and ID consistently exerting a negative impact on the GPP. Indices such as the CDI and DTR, while exhibiting an overall suppressive effect, demonstrate a declining trend in their influence over time. Conversely, several other indices--such as the ETI, RDI, and HPI--maintain stable and positive impacts across the study period. This indicates that while the effects of certain ECIs weaken with time, others remain persistently favorable for ecosystem functions, reflecting the region-specific responses under evolving climatic conditions. Nevertheless, the complex topography of SWC necessitates a demarcation of the study area based on its diverse terrain types to enhance the understanding of the temporal stability of ECIs on EIs in various environments. In the HDMs, specific indices maintained their significance in moving window analysis, with emerging trends of intensification. Furthermore, the occurrence of extreme droughts has a significant impact on the carbon cycle and vegetation greenness in several regions across China, particularly in the Loess Plateau, resulting in a notable decline in the GPP [50]. These findings align with broader trends observed across China's semi-arid regions, where prolonged water scarcity coupled with elevated temperatures severely reduces vegetation growth. This underlines the urgent need for adaptive strategies to mitigate such compound impacts in ecologically sensitive regions like SWC. As depicted in Figure S3, only three indices (STI, RDI, and HPI) exhibited no significant fluctuations across the thirty-eight years, illustrating that climate change significantly impacts the HDMs, with numerous indices undergoing notable shifts. Primary indices related to lower temperatures, FD and ID, exhibited a particularly significant decline over time (\(p<0.001\)). In the mid-altitude YGP, only the frost-related indices (FD and ID) have considerable negative effects on the GPP, while other indices exhibit varied positive influences on the GPP, suggesting substantial temporal stability. The existing research suggests that continued warming could foster forest expansion, and positive correlations between precipitation and tree growth are evident on the southeast fringes of the Tibetan Plateau [51]. The trend analysis presented in Figure S5 demonstrates that the YGP exhibits additional indices (DTR, GSL, and ID) with insignificant trend variations compared to the HDMs. Notably,the impact of FD is markedly decreased, while ID lacks a clear trend of change. This indicates that the HDMs are more responsive to ECIs than the YGP at mid- to high altitudes. By integrating this with a moving correlation analysis (Figure 4), it is evident that the YGP's adaptability to extreme climates surpasses that of the HDMs, as indicated by the insignificant trend of DTR in the former, contrasting with the significant suppressing effect and changing trend in the latter. Based on these trends, it is inferred that global warming will likely continue foster vegetation growth in mid- to high-altitude regions, which possess robust adaptability to extreme climatic conditions. Furthermore, water-use efficiency significantly influences the annual fluctuations in the NDVI and GPP. [PERSON] et al. [42] demonstrated that the responses of the NDVI and GPP to drought and precipitation conditions exhibited notable discrepancies, particularly in years characterized by higher water-use efficiency. In such years, the correlation between the GPP and NDVI was more pronounced, whereas this correlation diminished during years of reduced precipitation. Additionally, the long-term changes in soil moisture and surface runoff are pivotal factors influencing the interannual fluctuations in the NDVI and GPP. [PERSON] et al. [52] demonstrated that the augmented soil moisture was markedly correlated with the interannual stability of vegetation.