## 2 Study Area and Dataset
### Dataset  
The GPP dataset based on the LUE model by improving the optimal temperature for vegetation growth was used in this study, which could be calculated by Equation (1). The spatial resolution of these data is 0.05\({}^{\circ}\), and the time range is from 2001 to 2018. The resampling method is used to adjust the spatial resolution to 0.1\({}^{\circ}\). This dataset has been validated within R\({}^{2}\) and RMSE of 0.73\(\sim\)0.76 and 40 gCm\({}^{-2}\)mon\({}^{-1}\) (1.3 gCm\({}^{-2}\)d\({}^{-1}\)), indicating a better simulation accuracy [29].  
\[GPP=PAR\times FPAR\times\varepsilon_{\max}\times\frac{1.1814\times(1+\rho^{0.3 \times(-T_{opt}-10+T_{air})})}{1+\rho^{0.2\times(\Gamma_{opt}-10-T_{air})}} \times(0.25+0.75\times\frac{ET}{RN}) \tag{1}\]  
where \(PAR\) is photosynthetically active radiation; \(FPAR\) is fraction of photosynthetically active radiation; \(\varepsilon_{\max}\) is efficiency of light energy conversion under ideal conditions; \(T_{opt}\) is the optimum temperature for vegetation growth; \(ET\) is the actual evapotranspiration; \(RN\) is surface net radiation.  
In addition, the meteorological data including temperature, precipitation, vapor pressure deficit, and short-wave radiation used in this study were obtained from the China Meteorological Forcing Dataset, which is developed by the Institute of Tibetan Plateau Research, Chinese Academy of Sciences [30]. The time range used is from January 2001 to December 2018 with the spatial resolution 0.1\({}^{\circ}\). The historical CO\({}_{2}\) concentration data were  
Figure 1: Overview of the Yangtze River Basin, including 11 sub basins (F01: Jinsha River, F02: Mintuo River, F03: Jialing River, F04: Wujiang River, F05: Upper trunk stream, F06: Dongting Lake, F07: Hanjiang River, F08: Poyang Lake, F09: Middle trunk stream, F10: Lower trunk stream, F11: Taihu Lake).  
also obtained from the Wariguan Global Atmospheric Background Station, Global Monitoring Laboratory, National Oceanic and Atmospheric Administration (NOAA), Hainan Prefecture, Qinghai Province, China. It is the only atmospheric background observation station in the Northern Hemisphere, and its observation results can represent the atmospheric greenhouse gas concentration and its changes in the middle latitudes of the Northern Hemisphere. The land use data used are obtained from European Space Agency CCI-LC products ([[https://www.esa-landcover-cci.org/](https://www.esa-landcover-cci.org/)]([https://www.esa-landcover-cci.org/](https://www.esa-landcover-cci.org/)), accessed on 1 September 2023).  
To predict the future GPP in the Yangtze River Basin, the projected future climate data including daily precipitation, temperature, relative humidity, and radiation data are obtained from the selected GCMs under four Shared Socioeconomic Pathways (SSP) scenarios including SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 from Coupled Model Intercomparison Project Phase 6 (CMIP6). Meanwhile, the future elevated CO\({}_{2}\) data are from the National Data Center for Ecological Sciences [31]. This dataset is based on historical fossil fuel CO\({}_{2}\) emissions and monthly average CO\({}_{2}\) concentration data. For the average CO\({}_{2}\) concentration under the SSP-RCPs scenario from 2015 to 2150, based on the historical spatial distribution of CO\({}_{2}\) concentration, the monthly spatial distribution data of CO\({}_{2}\) concentration in the next 2015-2150 years under different scenarios were obtained.