## 3 Results and Analysis  
### Spatial and Temporal Distribution Characteristics of EVI and GPP  
The spatial distribution and trends of the Enhanced Vegetation Index (EVI) and Gross Primary Productivity (GPP) across China from 2001 to 2020 are depicted in Figure 2. Both indices exhibit higher values in the southeast and lower values in the northwest. The multi-year average EVI ranges from 0 to 0.64 (Figure 2a), with an annual change slope between \(-0.0033\) and \(0.0051\) per year (Figure 2c). The multi-year average GPP ranges from 0 to 408.85 gC/m\({}^{2}\).a (Figure 2b), with an annual change slope ranging from \(-4.64\) to \(3.98\) gC/m\({}^{2}\).a (Figure 2d). Higher growth rates are observed in humid and semi-humid regions, while lower or declining rates are evident in other regions. On a national scale, regions with decreasing EVI account for 15.95%, while those with increasing EVI account for 84.05%. In different climate zones, the proportions of decreasing regions are 34.45% in arid areas, 11.16% in semi-arid areas, 11.82% in semi-humid areas, and 4.2% in humid areas. Regarding land cover types, the proportions of decreasing regions are 4.49% in croplands, 3.98% in forests, 2.17% in shrubs, 13.76% in grasslands, and 37.29% in wetlands. For GPP, on a national scale, decreasing regions account for 34.11%, while increasing regions account for 65.89%. In different climate zones, the proportions of decreasing regions are 77.23% in arid areas, 28.38% in semi-arid areas, 8.12% in semi-humid areas, and 12.3% in humid areas. In terms of land cover types, the proportions of decreasing regions are 13.24% in croplands, 6.56% in forests, 3.14% in shrubs, 27.76% in grasslands, and 21.62% in wetlands. Overall, both EVI and GPP are predominantly increasing at the national level. However, significant decreases are observed in specific regions and land cover types, such as arid areas and wetlands (Figure 3). Figure 4 illustrates the inter-annual variations in EVI and GPP across China and various climatic zones from 2001 to 2020, revealing an overall increasing trend for both parameters. The annual rate of change for EVI is 0.001277 per year (Figure 4a), while for GPP, it is 0.933684 gC/m\({}^{2}\)/year (Figure 4f). Notably, significant differences in the inter-annual rates of change for EVI and GPP are observed among different climatic zones. In arid regions, the inter-annual rates of change are 0.000332 per year for EVI and 0.22109 gC/m\({}^{2}\)/year for GPP (Figure 4b,g). Semi-arid regions exhibit rates of 0.000913 per year for EVI and 0.500985 gC/m\({}^{2}\)/year for GPP (Figure 4c,h). Semi-humid regions show rates of 0.001617 per year for EVI and 1.109586 gC/m\({}^{2}\)/year for GPP (Figure 4d,i). Humid regions demonstrate the most pronounced increases, with rates of 0.002198 per year for EVI and 1.420436 gC/m\({}^{2}\)/year for GPP (Figure 4e,j). In summary, both EVI and GPP exhibit positive trends at the national level, with the most significant growth in humid regions and relatively slower growth in arid regions. Figure 3: Variation trends of EVI and GPP in different climate regions and land cover types (**notes**: WR: whole region; AR: arid region; SAR: semi-arid region; SHR: semi-humid region; HR: hu-mid region). Figure 2: Spatial distribution and Slope values of EVI and GPP (**notes**: (**a**): EVI spatial distribution; (**b**): GPP spatial distribution; (**c**): EVI Slope value; (**d**): GPP Slope value). The inter-annual variations in EVI and GPP for different land cover types from 2001 to 2020 are illustrated in Figure 5. These trends are consistently positive across all land cover types, indicating a gradual enhancement in ecosystem productivity and an improvement in ecosystem health.