## 4 Discussion  
### Spatiotemporal Variations and Correlations of RSM, PRE, and GPP  
Over recent decades, global vegetation GPP has exhibited an upward trajectory [50], with dryland ecosystems contributing more substantially to this global GPP increase than the overall greening observed worldwide between 1982 and 2015 [51]. Specifically, from 2000 to 2022, the summer annual mean GPP in China's arid and semi-arid regions demonstrated a significant positive trend, increasing at a rate of 0.4549 gCm\({}^{-2}\)yr\({}^{-1}\) (Figure 3a). Between 2007 and 2021, GPP trends varied spatially: increases were observed in portions of the Northeast China Plain, North China Plain, and the transitional zone between the Loess Plateau and Qaidam Basin, whereas declines occurred on the Tibetan Plateau and in the Turpan Basin, attributable to diminished vegetation development [23]. As illustrated in Figure 3a, the eastern sector of the study area exhibited more pronounced GPP growth, while the southwestern (Tibetan Plateau) and northwestern (Turpan Basin) regions showed decreasing trends, corroborating previous findings. Amidst a global drying trend, only approximately 10% of regions experienced significant increases in RSM, predominantly located in India, Bangladesh, South Asia, East Africa, and northwestern South America [10]. These areas with rising RSM were generally situated at higher elevations within arid and semi-arid zones [52]. Within the study region, 59% of the area displayed increasing RSM trends, whereas 41% exhibited declines, albeit with smaller magnitudes, culminating in an overall upward trend in RSM across the region. [PERSON] et al. (2018) analyzed extreme precipitation patterns in China's arid and semi-arid zones using data from 166 meteorological stations spanning 1960 to 2018, revealing precipitation instability, particularly pronounced in semi-arid areas, primarily driven by atmospheric circulation dynamics and topographic influences [53]. Temporally, the study identified a fluctuating pattern in summer mean  
Figure 8: The sensitivity of RSM and PRE to acidity gradients, with (**a**) illustrating the impact of RSM (\(\Delta SA_{CPP}(SA_{RSM}\,|\,SA_{PRE})\)) along aridity gradients, (**b**) showing the influence of PRE (\(\Delta SA_{CPP}(SA_{PRE}\,|\,SA_{RSM})\)) across aridity gradients, and (**c**) displaying GPP variations under different drought conditions. PRE without significant directional change (Figure S1f), consistent with these prior observations. Spatially, the eastern portion of the study area showed increasing summer PRE trends, whereas the western sector, notably the Tibetan Plateau, exhibited declining trends. Previous research has attributed the increased summer PRE in eastern Inner Mongolia to low-tropospheric moisture transport modulated by interactions betweenesterly winds and monsoonal flows, as well as upper-tropospheric dynamic forcing linked to variations in the westerly jet stream [54]. Furthermore, studies indicate that the southern and eastern Tibetan Plateau have experienced decreasing summer precipitation trends, potentially resulting from alterations in atmospheric circulation patterns and heterogeneous surface warming; notably, the southern plateau has undergone significantly greater warming than northern areas, thereby intensifying local circulation disparities [55]. The soil-vegetation-atmosphere system encompasses intricate and interrelated processes, necessitating a thorough elucidation of the coupling dynamics between RSM and PRE before assessing their individual influences on GPP [18; 56]. Although PRE constitutes the direct source of RSM, the quantity and stability of PRE in China's arid and semi-arid regions are limited and variable. As depicted in Figure 4d, the mean correlation coefficient between PRE and RSM was 0.42, indicating a positive yet moderate association between these variables.