## 3 Evaluation of Remote Sensing Products and GPP Simulations
The average Bias values for the BGCDV_CTL experiment and the BGCDV_NEW experiment were 0.003 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) and \(-0.017\) gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\), respec  
Figure 2: Model simulations from CLM5.0-DGVM versus observations of daily GPP (unit: gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\)), NEE (unit: gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\)), and Re (unit: gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\)) at Dangx from 2007 to 2010, Haibei from 2003 to 2007, and Maqu from 2010 to 2019; the black, blue, and red lines are the means from observation, the BGCDV_CTL experiment, and the BGCDV_NEW experiment, respectively. tively. After modifying the seasonal-deciduous phenology parameterization, the simulated Re tended to reduce at the Dangx site. The RMSE reduced from 0.323 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) to 0.300 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\), and Corr increased from 0.899 to 0.915. Compared to the BGCDV_CTL experiment, the average Bias and RMSE of the simulated GPP in the BGCDV_NEW experiment reduced from \(-0.136\) gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) and 1.227 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) to \(-0.109\) gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) and 1.127 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\), respectively, and Corr increased from 0.863 to 0.882. The dramatic increase in the simulated GPP from May to June was mainly caused by the increase in the simulated NEE. The simulated NEE from the BGCDV_NEW experiment had a better performance than that from the BGCDV_CTL experiment. At the Haibei site, the simulated Re underestimated the observed Re during the non-growing seasons and overestimated Re in autumn (September to November). The average Bias of the simulated Re by the BGCDV_NEW experiment decreased by 21%, and seasonal variations in the BGCDV_NEW experiment coincided better with observations. The simulated NEE from the BGCDV_NEW experiment tended to overestimate NEE during the non-growing season and reduced the biases of NEE during the growing season at the Maqu site. The average Bias and RMSE of the simulated NEE in the BGCDV_NEW experiment reduced from 0.366 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) and 1.114 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) to 0.355 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) and 0.877 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\), respectively, and Corr increased from 0.634 to 0.814. The BGCDV_CTL experiment tended to overestimate Re, and the average Bias between the BGCDV_CTL experiment simulations and observations was 0.606 gC\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\). In addition, obvious systematic errors existed at the Dangx and Haibei sites from July to September, which may have been caused by the imperfections of the water use efficiency parameterization scheme. The simulated carbon flux of CLM5.0-DGVM is sensitive to water content and less sensitive to temperature. According to PBIAS, the simulated GPP at the Dangx, Haibei, and Maqu sites are considered acceptable. The Re simulations are satisfactory at the Dangx and Haibei sites, and the simulated NEE at the Dangx, Haibei, and Maqu sites are considered unacceptable. The Maqu and Haibei sites are located in the eastern and northern regions of the TP, respectively, and both sites are obvious carbon sinks, while the Dangx site is a weaker carbon source that is located in the central region of the TP and at a high elevation. At the Maqu and Haibei sites, with rich soil organic matter, the photosynthetic carbon absorption during the growing season is higher than that of the Dangx site. Compared to the Maqu and Haibei sites, the observed GPP and Re are smaller at the Dangx site. Figure 3 shows the monthly variations in the simulated GPP from CLM5.0-DGVM and the NIRv, GLASS, FLUXCOM, and MODIS products versus observations at the Dangx, Haibei, and Maqu sites. The GPP provided by NIRv underestimated the growing season length at the Dangx site, mostly due to a delayed start of the growing season. At the Haibei and Maqu sites, the NIRv GPP product overestimated GPP in the growing season.