## 3 Results  
### Spatiotemporal Variations of GPP and WUE  
Figure 2 presents the spatial distribution of the multi-year average GPP and WUE across China from 2001 to 2021. Both exhibited manifest patterns of spatial variation (Figure 2a,d) and were in good agreement with the division of each arid-humid zone. Specifically, the average GPP and WUE across China from 2001-2021 were 692.65 gC\(\cdot\)m\({}^{-2}\) and 1.17 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), respectively. GPP decreased gradually from the humid zone to the arid zone (Figure 2b), with the humid zone (1083.75 gC\(\cdot\)m\({}^{-2}\)) being 5.6 times higher than the arid zone (192.20 gC\(\cdot\)m\({}^{-2}\)). The distribution pattern of WUE was similar to that of GPP, but the value in the arid zone (0.84 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) is slightly higher than the semi-arid zone (0.78 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) (Figure 2e), and the WUE in the humid zone (1.43 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) was about twice as high as that in the arid and semi-arid zones. Among all vegetation types, forest and cropland had higher GPP and WUE values of 1172.16, 756.95 gC\(\cdot\)m\({}^{-2}\) and 1.52, 1.43 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), respectively (Figure 2c,f). These two vegetation types occupied most areas of the humid zone (68.44%) and the semi-humid  
Figure 2: Spatial distribution of (**a**) multi-year average GPP (units: gC\(\cdot\)m\({}^{-2}\)) and (**d**) WUE (units: gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) during 2001–2021. (**b,e**) represent multi-year average GPP and WUE for each arid-humid zone, (**c,f**) represent multi-year average GPP and WUE for each vegetation type. zone (39.43%), which were the main contributors to the GPP and WUE values in these two zones (Table S1). In contrast, grassland occupied most of the area in semi-arid regions (73.20%), but it had relatively small GPP (299.30 gC\(\cdot\)m\({}^{-2}\)) and WUE (0.81 gC\(\cdot\)m\({}^{-2}\)-mm\({}^{-1}\)). The shrubland had the lowest GPP (291.25 gC\(\cdot\)m\({}^{-2}\)) and WUE (0.62 gC\(\cdot\)m\({}^{-2}\)-mm\({}^{-1}\)) values among all vegetation types in China, while wetland GPP (327.64 gC\(\cdot\)m\({}^{-2}\)) and WUE (0.64 gC\(\cdot\)m\({}^{-2}\)-mm\({}^{-1}\)) values were in the middle level. In general, the distribution of GPP and WUE across China had a strong geographical zonality along the aridity gradient, while, specifically within each vegetation type, they showed a more complex distribution of values. A statistical analysis of GPP across China within the study years revealed a remarkable upward trend in GPP from 2001 to 2021 (6.41 gC\(\cdot\)m\({}^{-2}\)-yr\({}^{-1}\)). In comparison, the national WUE increased at a lower rate, with an average variation value of 0.0016 gC\(\cdot\)m\({}^{-2}\)-mm\({}^{-1}\).yr\({}^{-1}\) (Figures 3 and S1). Figures 4 and 5 provide detailed statistics on the temporal changes of GPP and WUE in each arid-humul zone and vegetation type from 2001 to 2021. Regarding the variation of GPP, a significant upward trend was observed in all arid-humul zones and vegetation types (Figures 4a and 5a). In each arid-humul zone, the greatest upward trend of GPP was displayed in the humid and semi-humul zones, with 7.63 and 7.56 gC\(\cdot\)m\({}^{-2}\)-yr\({}^{-1}\), respectively. Arid and semi-arid zones showed a lower increase in GPP than humid and semi-humul zones (Figure 3). The tendency of increasing GPP was greatest in forest and cropland (7.91 and 8.71 gC\(\cdot\)m\({}^{-2}\)-yr\({}^{-1}\)) among all vegetation types, with the increasing trend in cropland being significantly greater than that in forest. From the area proportion of GPP in increasing regions around the country (Figures 4b and 5b), the area proportions of increasing GPP in each arid-humul zone and vegetation type all reached more than 90% except for wetland, and the significantly increased regions (\(p<0.05\)) also remained an area proportion of more than 50%.