## 2 Materials and Methods  
### Carbon Flux  
We downloaded meteorological and CO\({}_{2}\) flux data collected by eddy covariance towers from the FLUXNET2015 Dataset Tier 1 ([[https://fluxnet.org/data/fluxnet2015-dataset/](https://fluxnet.org/data/fluxnet2015-dataset/)]([https://fluxnet.org/data/fluxnet2015-dataset/](https://fluxnet.org/data/fluxnet2015-dataset/)), accessed on 25 February 2023) available from 2000 to 2014. We used the daily mean radiation data estimated from average half-hourly records (SW_IN) and daily values of GPP based on methods of daytime partitioning (GPP_DT_VUT_USTAR50) [29].  
We selected 26 sites that fulfilled the criteria of (i) high-quality continuous data and (ii) homogeneous vegetation types in pixel areas to match satellite data (Figure 1, Table 1). Site homogeneity in an area of 1 \(\times\) 1 km\({}^{2}\) was visually evaluated using high-resolutionsatellite images in Google Earth. Sites with homogeneous land cover were selected at high (53-70 degN, 5 sites), middle (45-53 degN, 9 sites) and low (30-45 degN, 12 sites) latitudes, with eight vegetation cover types: evergreen needleleaf forest (ENF, 10 sites), evergreen broadleaf forest (EBF, 2), deciduous broadleaf forest (DBF, 7), mixed forest (MF, 2), open shrubland (OSH, 2), grassland (GRA, 1), woody savanna (WSA, 1) and wetland (WET, 1). Vegetation cover types were provided by FLUXNET using the International Geosphere-Biosphere Programme (IGBP) land classification ([[https://fluxnet.org/data/badm-data-templates/igbp-classification/](https://fluxnet.org/data/badm-data-templates/igbp-classification/)]([https://fluxnet.org/data/badm-data-templates/igbp-classification/](https://fluxnet.org/data/badm-data-templates/igbp-classification/)), accessed on 25 February 2023).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Site ID** & **Latitude (°)** & **Longitude (°)** &
\begin{tabular}{c} **Vegetation** \\ **Cover Type** \\ \end{tabular} & **Time Period** \\ \hline CA-NS6 & 55.9 & \(-\)99.0 & OSH & 2001–2005 \\ CA-SF2 & 54.3 & \(-\)105.9 & ENF & 2001–2005 \\ CA-SF3 & 54.1 & \(-\)106.0 & OSH & 2001–2006 \\ CH-Lae & 47.5 & 8.4 & MF & 2004–2014 \\ CZ-BK1 & 49.5 & 18.5 & ENF & 2004–2014 \\ DE-Obe & 50.8 & 13.7 & ENF & 2009–2014 \\ DE-Spw & 51.9 & 14.0 & WET & 2010–2014 \\ DE-Tha & 51.0 & 13.6 & ENF & 2000–2014 \\ FI-Hyy & 61.8 & 24.3 & ENF & 2000–2014 \\ FR-Fon & 48.5 & 2.8 & DBF & 2005–2014 \\ FR-LBr & 44.7 & \(-\)0.8 & ENF & 2000–2008 \\ FR-Pue & 43.7 & 3.6 & EBF & 2000–2014 \\ IT-Cpz & 41.7 & 12.4 & EBF & 2000–2008 \\ IT-Ro1 & 42.4 & 11.9 & DBF & 2000–2008 \\ IT-Sko & 43.7 & 10.3 & ENF & 2000–2012 \\ JP-MBF & 44.4 & 142.3 & DBF & 2004–2005 \\ JP-SMF & 35.3 & 137.1 & MF & 2005–2006 \\ NL-Loo & 52.2 & 5.7 & ENF & 2005–2014 \\ RU-Fyo & 56.5 & 32.9 & ENF & 2000–2014 \\ US-Ha1 & 42.5 & \(-\)72.2 & DBF & 2007–2009 \\ US-Me6 & 44.3 & \(-\)121.6 & ENF & 2000–2012 \\ US-UMS & 39.3 & \(-\)86.4 & DBF & 2011–2014 \\ US-SRG & 31.8 & \(-\)110.8 & GRA & 2000–2014 \\ US-SRM & 31.8 & \(-\)110.9 & WSA & 2008–2014 \\ US-UMB & 45.6 & \(-\)84.7 & DBF & 2004–2014 \\ US-UMd & 45.6 & \(-\)84.7 & DBF & 2000–2014 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Coordinates, vegetation cover type and time period of data used in the studied sites. OSH (open shrubland), ENF (evergreen needleleaf forest), MF (mixed forest), WET (wetland), DBF (deciduous broadleaf forest), EBF (evergreen broadleaf forest), GRA (grassland) and WSA (woody savanna).  
Figure 1: Sites used in this study.