## 2 Materials and Methods
### Remote Sensing Products and Processing  
The BESS is designed to continuously measure global carbon and water fluxes [29] and provides the global 1 km resolution GPP product with an interval of eight days during the period from 2000 to 2015. In the BESS-derived GPP, radiation, photosynthetic active radiation, and near-infrared radiation \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Site Name** & **Location** & **Altitude** & **Observation** & **Vegation Type** & **Mean** & **Precipitation** & **Available Years** \\  & & **(m)** & **Height (m)** & **Temperature\({}^{\circ}\)C** & **(mm)** & **Available Years** \\ \hline A’rou & 100.4643\({}^{\circ}\) E & 3033 & 3.5 & Alpine meadow & \(0.03\pm 0.62\) & 460 \(\pm\) 63 & 2014.01–2016.12 \\  (S\_Ar) & 38.0473\({}^{\circ}\) E & 3033 & 3.5 & Alpine meadow & \(0.03\pm 0.62\) & 460 \(\pm\) 63 & 2014.01–2016.12 \\  (S\_Dm) & 30.3722\({}^{\circ}\) E & 1556 & 4.5 & Maize cropland & \(6.92\pm 0.16\) & 129 \(\pm\) 26 & 2014.01–2016.12 \\  (S\_Dsl) & 38.8595\({}^{\circ}\) N & 3739 & 4.5 & Swamp meadow & –3.96 \(\pm\) 0.47 & 341 \(\pm\) 41 & 2014.01–2016.12 \\  (S\_Hhl) & 101.335\({}^{\circ}\) E & 874 & 22 & Populus euphratica & \(10.38\pm 0.14\) & 34 \(\pm\) 17 & 2014.01–2016.12 \\  (S\_Sd) & 41.9003\({}^{\circ}\) N & 873 & 8 & Tamarix & \(9.36\pm 0.11\) & 33 \(\pm\) 9 & 2014.01–2016.12 \\  (S\_Sd) & 42.0012\({}^{\circ}\) N & 873 & 8 & Tamarix & \(9.36\pm 0.11\) & 33 \(\pm\) 9 & 2014.01–2016.12 \\   Zhangey & 100.446\({}^{\circ}\) E & 1460 & 5.2 & Wetland & \(9.45\pm 0.34\) & 95 \(\pm\) 24 & 2014.01–2016.12 \\  (S\_Zy) & 38.9751\({}^{\circ}\) N & & & & & & \\ \hline \hline \end{tabular} The mean temperature represents the average daily temperature from 2014 to 2016 and precipitation represents cumulative average annual precipitation from 2014 to 2016 for each flux site. The standard deviations of mean temperature and precipitation are also attached.  
\end{table} 
Table 1: Descriptions of the flux sites used in this study. at the top of the canopy were calculated by an atmospheric radiative transfer model, and then these parameters, absorbed by the sunlit and shade leaves, were gained by a two-leaf canopy radiative transfer model. Furthermore, it used the biochemical photosynthesis models for C\({}_{3}\) and C\({}_{4}\) plants, and parameterized maximum carboxylation rate based on plant functional type, climatic zones, and the season. The BESS products used seven MODIS atmospheric and land products, four other satellites, four reanalyses, and three auxiliary datasets. We used the MODIS GPP version 6 (MOD17A2H) obtained from the Terra platform, with 500 m spatial resolution [36], which is produced using the LUE model as follows:  
\[\mathrm{GPP}=\mathrm{LUE}_{\mathrm{max}}\times\mathrm{f}(\mathrm{T}_{ \mathrm{MIN}})\times\mathrm{f}(\mathrm{VPD})\times\mathrm{SWRad}\times 0.45 \times\mathrm{FPAR} \tag{1}\]  
where \(\mathrm{LUE}_{\mathrm{max}}\) is the maximum value of light use efficiency, while SWRad denotes incident shortwave radiation. \(\mathrm{T}_{\mathrm{min}}\) is the daily minimum temperature, VPD is the daylight average vapor pressure deficit, and FPAR is the fractional photo-synthetically active radiation absorbed by the canopy. The algorithm logic and model parameters can also be found in the MOD17 user guide [38]. The model assumed that the GPP is proportional to plant absorption and effective radiation under ideal conditions [39]. A set of biome-specific radiation-use efficiency parameters was acquired from the updated Biome Property Look Up Tables. The product also used a new version of the daily Global Modeling and Assimilation Office (GMAO) meteorological data [39]. The product used in this study was downloaded from NASA's Earth Observing System Data and Information System ([[https://search.earthdata.nasa.gov](https://search.earthdata.nasa.gov)]([https://search.earthdata.nasa.gov](https://search.earthdata.nasa.gov))). We re-sampled it to 1 km pixel size before being extracted based on site locations.