## 4 Discussion
### Temporal Stability of ECIs and Their Impacts on Ecosystem at the Annual Scale
In the context of ecological restoration on the Loess Plateau, the effective replenishment of soil moisture significantly enhances the NDVI and GPP. Climate change exerted a relatively minor effect on the GPP in the SCB, but its influence on the NDVI is more pronounced, showing a stable negative correlation with temperature-associated indices. The underlying cause of this may be the increased vapor pressure deficit induced by warming. This deficit can curtail photosynthetic activity and exacerbate carbon starvation in vegetation by diminishing stomatal conductance and enhancing non-photochemical quenching [53; 54; 55; 56]. The basin's geographic positioning, surrounded by higher terrain with a lower central area, facilitates persistent water vapor, which, coupled with reduced sunlight and photosynthetically active radiation [57; 58] and a trend of increasing precipitation intensity [24], could impact photosynthetic efficacy [59]. The impacts of extreme climate events on vegetative productivity in the SCB may be mediated by the locale's topography and the ambient regional climate. ECIs are weakly correlated with the GPP but have a notable impact on the NDVI, with significant increases in high-temperature indices such as the ETI and SU (\(p<0.001\)) (Figure S4) presenting a negative temporal correlation with the NDVI. The predominance of local crops, which are subject to significant human interaction [60], suggests that warming trends may expedite agricultural growth cycles, reduce developmental duration, and thus diminish canopy radiation absorption, ultimately impacting biomass accumulation and yield [61; 62]. In the GXB, the DTR, SU, and TR superseded precipitation as the pivotal factors influencing the GPP. Characterized by regional thermal profiles and variations, these indices exhibit commendable temporal stability. The basin's geography, with its central and southern regions consisting predominantly of hills, supports converged water flows and substantial rainfall, providing ample surface water resources that are conducive to groundwater storage and vegetative growth [63]. Moreover, due to its proximity to the South China Sea, local temperatures are closely connected to sea surface temperature anomalies and atmospheric interactions [64; 65; 66; 67; 68]. Notably, the GXB reported the least significant alterations in the ECIs (Figure S6). A moving correlation analysis highlights that the DTR and SU exhibit consistent temporal stability in their impacts on GPP, despite showing opposite trends. This suggests that rising temperatures (reflected by the SU) may gradually promote photosynthetic activity, while the decreasing diurnal temperature range (DTR) reduces the stress caused by the extreme daily temperature fluctuations. Compared to mid-high-altitude regions, the NDVI in the GXB responds less strongly to ECIs (Figure 4h), underscoring the region's inherent resilience to climatic variability due to factors such as adequate water resources and minimal temperature extremes. These findings highlight the distinct adaptation mechanisms of GXB ecosystems, particularly in terms of their ability to withstand both warming and fluctuating precipitation patterns.