# Decoupling the Impacts of Climate Change and Human Activities on Terrestrial Vegetation Carbon Sink
## 4 Discussion  
### NEP Changes Caused by CC and HA  
Investigating how ongoing CC affects NEP is crucial for understanding carbon cycling dynamics. Overall, NEP in CCZ shows a spatial distribution with higher values in the south and lower values in the north. The regions exhibiting an increasing trend in NEP account for 74.81% of the total area. Coastal areas have undergone a warming trend in the past two decades, and temperature and NEP exhibit a positive correlation in 82.6% of the regions, indicating that climate warming broadly promotes the increase in NEP across CCZ. This is because a moderate rise in temperature resulted in a more significant increase in NPP compared to increases in soil respiration [40]. Figures 6 and 7 illustrate the partial correlation results between NEP and precipitation, and the areas with positive and negative correlation coefficients exhibit nearly identical distribution patterns, meaning that precipitation mainly dominates the spatial heterogeneity of NEP in coastal areas to a large extent. [PERSON] et al. found that variations in rainfall dominated annual dynamics in NEP across China [41]. Additionally, [PERSON] et al. showed that maximum five-day precipitation in China's coastal areas enhanced vegetation growth in the northern regions but had an adverse impact in the south [42]. So, NEP in coastal areas may be influenced not only by annual precipitation variation but also by seasonal precipitation intensity. Specifically, NEP in the Beijing-Tianjin-Hebei region, parts of Liaoning Province, and most areas of Shandong Province exhibited a significant increase trend mainly attributed to the positive effects of hydrothermal conditions. Moreover, we found HA here also promoted the increase in NEP, which may be attributed to the ecological engineering projects in these regions since 2000, like the Grain for Green Project, Three-North Shelterbelt Forest Program, and Beijing-Tianjin Sand Source Control Program [43]. China's endeavors in ecological restoration were predominantly shaped by anthropogenic factors and have been proven to significantly facilitate the increase in ecosystem service values [44]. Moreover, [PERSON] et al. found that both temperature and precipitation in the Beijing-Tianjin-Hebei region showed a significant positive correlation with NPP, with precipitation identified as the key driving factor [45], which is in line with our results. The North China Plain is a major region for crop production in China with a large cultivated area [46], which provides more than 10% of China's total grain [47]. As depicted  
Figure 12: Area proportion of NEP diver types. in Figures 5 and 8, our results indicated a significant rising trend of NEP in the majority of the NCP, which is mainly attributed to the combined positive effects of CC and HA. As [PERSON] et al. indicated, the productivity of crops in the NCP is sensitive to both climate conditions and agricultural management practices [48]. We found that both temperature and precipitation in the NCP are positively correlated with NEP. The reason why HA promotes the increase in NEP here may be attributed to modern agriculture [49]. Despite the upward trend in NEP, [PERSON] et al. proposed that ozone pollution caused an average 25% decline in NPP in the NCP [50]. Meanwhile, the cropping structure could also affect the carbon balance of agricultural ecosystems [51], and maize-based cropping systems are considered more advantageous for both biomass and economic benefits in the NCP compared to other cropping systems [52]. As shown in Figures 2 and 5, our results showed that most of the negative and degraded NEP occurred in areas around core cities with higher urbanization levels, especially in Guangdong and Jiangsu. According to statistical data, the GDP of Guangdong and Jiangsu consistently ranks first and second nationwide, making them the two most economically developed provinces. [PERSON] et al.