## 4 Results
### Future Projection of GPP Changes under Different Scenarios
Under SSP3-7.0 scenario, the following is shown: in spring, the area below 100 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, and most of them are concentrated in the Jinsha River; the area between 100-200 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, and the area above 200 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 60%, which is mainly concentrated in the Jialing River, upper trunk stream, and Hanjiang River; in summer, the area below 200 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 50%, mostly concentrated in the Poyang Lake, Dongting Lake, and the lower reaches of the Yangtze River; the area between 200 and 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, mostly concentrated in the Jinsha River; the area above 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 30%, mostly concentrated in the Jialing River and the Hanjiang River. In autumn, the area below 100 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, and most of them are concentrated in the Jinsha River; the area between 100-300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 60%, and the area above 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, most of which are concentrated in the southwest of the basin, the upper trunk stream, and Dongting Lake; in winter, 80% of regions have GPP below 100 gCm\({}^{-2}\)mon\({}^{-1}\). Under SSP5-8.5 scenario, the following is shown: in spring, the area below 100 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 15%, and most of them are concentrated in the Jinsha River; the area between 100-300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 15%, and the area above 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 60%, most of which are concentrated in the Jialing River, upper trunk stream, and Hanjiang River. In summer, the area below 200 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 40%, mostly concentrated in the Poyang Lake, Dongting Lake, and the lower reaches of the Yangtze River; the area between 200 and 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 15%, mostly concentrated in the Jinsha River. The area above 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 45%, mostly concentrated in the Jialing River and the Hanjiang River. In autumn, the area below 100 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 20%, and most of them are concentrated in the Jinsha River; the area between 100-300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 40%, and the area above 300 gCm\({}^{-2}\)mon\({}^{-1}\) accounts for about 40%, and most of them are concentrated in the southwest of the basin, the upper trunk stream, and Dongting Lake; in winter, 70% of the regions have GPP below 100 gCm\({}^{-2}\)mon\({}^{-1}\). To further investigate the variations in GPP across different sub basins of the Yangtze River Basin in the future, the changes between future and historical GPP are illustrated in Figure 15. Generally, GPP increases mostly in spring and autumn, while it shows less increase and even some decreases compared to the historical values in some sub basins in summer. In spring, the sub basins with large changes in GPP include the Jialing River, Wujiang River, upper trunk stream, and Hanjiang River, of which the upper trunk stream has the largest change, with 109.11, 193.24, 290.25, and 400.01 gCm\({}^{-2}\)mon\({}^{-1}\), respectively, under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios. In summer, the sub basins with great changes of GPP include the Mintuo River, Jialing River, the upper trunk stream, and the Hanjiang River. The Mintuo River has the largest change of 54.95 gCm\({}^{-2}\)mon\({}^{-1}\) under SSP1-2.6 scenarios, and the Hanjiang River has the largest change of 86.45, 135.73, and 202.43 gCm\({}^{-2}\)mon\({}^{-1}\) under SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios. Meanwhile, in the Dongting Lake, Poyang Lake, lower trunk stream, and Taihu Lake, GPP show small decreases compared to the historical values.