## 3 Results
### The Spatio-Temporal Variations of GPP and Climate Factors in the YRB  
We analyzed the overall changes of the GPP in the YRB spanning the years 2000 to 2018, which were depicted in Figure 4. The annual average GPP in the YRB fluctuated from 999.77 to 1275.60 g C m\({}^{-2}\) yr\({}^{-1}\), and the GPP reached the highest value in 2013. The annual average GPP increased significantly during the 19-year period (\(R^{2}\) = 0.54, \(p\) < 0.01), with an annual average GPP increase rate of 8.86 g C m\({}^{-2}\) yr\({}^{-1}\) per year. Figure 5a-b illustrated the spatio-temporal variations in the GPP change rate across the YRB during 2000-2018. Results showed that the change rate of GPP in the YRB mainly ranged from \(-\)26.55 to 36.99 g C m\({}^{-2}\) yr\({}^{-2}\), with an average of 9.01 \(\pm\) 8.31 g C m\({}^{-2}\) yr\({}^{-2}\). A total of 68.52% of the regions were significant at the significance level of \(p\) < 0.1, and the average \(R^{2}\) was 0.27 \(\pm\) 0.25. In addition, 87.74% of the YRB regions had increasing trends of GPP with an average GPP change rate of 10.80 g C m\({}^{-2}\) yr\({}^{-2}\). Among them, 73.71% of the regions were significant at the significance level of \(p\) < 0.1. A total of 12.26% of the YRB had decreasing trends with an average GPP change rate of \(-\)4.71 g C m\({}^{-2}\) yr\({}^{-2}\), but the results of regression  
Figure 3: Boxplot of the variations of GPP in different water resource regions (**a**), and vegetation types (**b**) in the YRB. Boxplot elements: square points = mean values; horizontal lines within boxes = medians; whiskers = 1.5 times of interquartile ranges; and points outside the boxes = outliers. analysis showed that 96.15% of those regions with negative slopes were not significant (\(p\) > 0.1). The regions with reduced GPP were primarily situated in the lower reaches of the Yangtze River and the headwater regions. We analyzed the change rate of GPP across various water resource regions and vegetation types in the YRB, as illustrated in Figure 5c-d. From the upper reaches to the lower reaches of the YRB, the GPP change rates of the 12 water resource regions presented an initial upward trend followed by a subsequent decline, as per the results in Section 3.1. The change rate of GPP was mainly positive in the upper reaches and finally became negative in the estuary, as shown in Figure 5c. The Jinsha River above Shigu (JSJ-1) had the lowest positive GPP change rate, which is 2.25 \(\pm\) 4.32 g C m\({}^{-2}\) yr\({}^{-2}\), followed by the Yangtze River mainstream below Hukou (LM), which is 3.45 \(\pm\) 7.08 g C m\({}^{-2}\) yr\({}^{-2}\). The Poyang Lake Basin (PYL), the Jialing River Basin (JLJ), and the Han River Basin (HJ) had relatively higher GPP growth rates, with averages of 13.98 \(\pm\) 7.07 g C m\({}^{-2}\) yr\({}^{-2}\), 13.81 \(\pm\) 7.69 g C m\({}^{-2}\) yr\({}^{-2}\), and 13.54 \(\pm\) 7.95 g C m\({}^{-2}\) yr\({}^{-2}\), respectively. The GPP in the Taiwan Lake Basin (TL) mainly showed decreasing trends, and the change rate of GPP was \(-\)4.22 \(\pm\) 9.85 g C m\({}^{-2}\) yr\({}^{-2}\). Only 27.71% of the Taihu Lake Basin (TL) had increasing GPP trends. GPP in the vegetation area showed increasing trends in the YRB (Figure 5d). Overall, savannas and forests had relatively higher GPP increasing rates, with averages of 13.07 \(\pm\) 6.79 g C m\({}^{-2}\) yr\({}^{-2}\) and 12.16 \(\pm\) 6.54 g C m\({}^{-2}\) yr\({}^{-2}\), respectively. Grassland had much lower GPP increasing rates with an average of 4.27 \(\pm\) 4.34 g C m\({}^{-2}\) yr\({}^{-2}\). Figure 4: The variations of annual average GPP (**a**), precipitation (**b**), temperature (**c**), and shortwave radiation (**d**) from 2000 to 2018 in the YRB. Figure 5: _Cont._  
We also investigated the spatio-temporal changes of climate factors in the YRB, as shown in Figure 4b-d and supplementary file (Figures S1-S3). We observed an increasing trend of precipitation in the YRB, but the trend of annual averages was not significant (_Slope_ = 4.21 mm yr\({}^{-2}\), \(p>0.1\), Figure 4b).