## 3 Results
### Climatic Effects on GPP and WUE  
Figure 8 gives the spatial trends of five major climatic factors in China from 2001 to 2021. RH, Rn, and WS mainly showed a decreasing trend nationwide, while Ta and Pr displayed a manifest increasing trend. Among the five climatic factors, RH varied from 2.03% to 0.93%, with a decreasing trend in approximately 90% of the regions except for central and northeastern parts of the semi-humid and semi-arid zones. Rn tended to decrease in 66% of the country, mainly in the humid, semi-humid, and semi-arid zones of central-eastern China. The variation of Ta across China from 2001 to 2021 ranged from \(-\)0.05 \({}^{\circ}\)C to 0.32 \({}^{\circ}\)C. Ta exhibited an upward trend throughout 97% of China, with significant increases in all regions except the central and northeastern semi-humid and semi-arid zones. Pr and WS varied from \(-\)32.05 to 48.71 mm and \(-\)0.16 to 0.14 m\(\cdot\)s\({}^{-1}\), respectively. Pr showed an increasing trend in 75% of the country. WS decreased in 73% of China, with a significant decrease in a larger proportion (55%). Details of the area proportion of change in each climatic factor during 2001-2021 can be found in Table S2. Figure 8: Spatial distribution of trend for each climatic variable across China from 2001 to 2021. (**a**) Relative Humidity (RH, units: % yr\({}^{-1}\)); (**b**) Net radiation (Rn, units: MW\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\)); (**c**) Average temperature (Ta, units: \({}^{\circ}\)C\(\cdot\)yr\({}^{-1}\)); (**d**) Precipitation (Pr, units: mm\(\cdot\)yr\({}^{-1}\)); (**e**) Wind Speed (WS, units: m\(\cdot\)s\({}^{-1}\cdot\)yr\({}^{-1}\)). Increased\({}^{*}\) Decreased\({}^{*}\): indicates the regions of significant increase or decrease (\(p<0.05\)). Figures 9 and 10 represent the spatial distribution of the correlation coefficients for GPP and WUE with each climatic factor. At the national scale, the average correlation coefficients of RH, Rn, Ta, Pr, and WS with GPP were \(-\)0.18, \(-\)0.06, 0.33, 0.19, and \(-\)0.16, respectively. Ta had the largest correlation coefficient with GPP and the trend was very consistent, as seen in the change curves of GPP and Ta over the period 2001-2021 (Figure S1). In all arid-humid zones and vegetation types (Figures 11 and 12), GPP showed a high positive correlation with temperature. Although GPP also performed a higher sensitivity to RH, it was mainly concentrated in humid and semi-humid zones and exhibited a negative correlation with RH compared to Ta (Figures 9 and 11). Besides Ta, GPP also positively correlated with Pr in all arid-humid zones and vegetation types, inferring that these were the two main climatic factors responsible for the upward trend of GPP from 2001 to 2021, but Ta contributed more to GPP than Pr. As can be seen in Figures 9 and 11, the correlation coefficient between GPP and Pr exceeded that of Ta only in the semi-arid zone. Moreover, GPP showed high correlation with Ta for all vegetation types except grassland. Of the other two climate factors, GPP was negatively correlated with Rn and WS in most arid-humid zones and vegetation types (Figures 11 and 12). The average correlation coefficient of GPP with WS was close to RH at the national level, but was not prominent in each dry and wet zone. (Figure 12). However, shrubland WUE showed similar magnitude of correlation coefficients with the five climatic factors, where it showed a higher positive correlation with RH. Wetland WUE had higher negative correlation values with Pr. Figures 13 and 14 further show the average correlation coefficients of GPP and WUE corresponding to each vegetation type with climatic factors in the four arid-humid zones. The specific values are presented in Tables S3 and S4. Similarly, we could find that the GPP for all vegetation in each arid-humid zone showed an obvious uniform positive and negative correlation with Ta and RH (Figure 13a,c). Rn and GPP exhibited a negative correlation in all arid-humid zones except for the humid zone, with the shrubland showing the most pronounced (Figure 13b).