## 5 Conclusions  
This is the first case study that combines in situ data from sugarcane EC flux towers and satellite (MODIS) images to estimate the GPP of sugarcane croplands using the VPM model. The sensitivity analyses between the GPP\({}_{\text{EC}}\) and vegetation indices (NDVI and EVI) at the two sites provide new insight into the biophysical performance of vegetation indices. The sensitivity analysis between the GPP\({}_{\text{EC}}\) and temperature variables, including the mean daily air temperature, mean daytime air temperature, land surface temperature, and the analysis between the EVI and temperature variables at the two sites provides a reasonable method for finding the optimum air temperature values at individual sites, which may improve VPM model simulations at the landscape scale. The results demonstrate that the VPM model performs well in estimating the GPP seasonal dynamics at the two sugarcane sites. The maximum LUE parameter value in this study (\(0.9\) g C mol\({}^{-1}\) PPFD) is reasonable for applying the VPM model at these sugarcane croplands. The linked analyses of the flux data (GPP\({}_{\text{EC}}\)) from the EC flux tower sites, predicted GPP (GPP\({}_{\text{VPM-Site}}\)) with in-situ climate data from the EC flux  
Figure 10: A comparison of the seasonal variation in the estimated GPP\({}_{\text{EC}}\) and predicted GPP\({}_{\text{VPM-Site}}\), GPP\({}_{\text{VPM-NCEP}}\), GPP\({}_{\text{VPM-Glo}}\), and GPP\({}_{\text{VPM-Globe}}\) at the two sugarcane EC tower sites. (**a,c**), Brazil site, 2005–2007; (**b,d**), Louisiana, USA site, 2017.  
tower site, and predicted GPP (GPPVPM-NCEP) with the NCEP climate data clearly demonstrates the feasibility of the VPM model to estimate and predict sugarcane physiological parameters in different climate systems. Additional evaluations of the VPM model at other sugarcane EC flux tower sites are still needed, which would contribute to a better understanding of the potential sources of errors and uncertainty in the simulations of the VPM model. The following are available online at [[http://www.mdpi.com/2072-4292/12/14/2186/s1](http://www.mdpi.com/2072-4292/12/14/2186/s1)]([http://www.mdpi.com/2072-4292/12/14/2186/s1](http://www.mdpi.com/2072-4292/12/14/2186/s1)), Figure S1: Averaged sugarcane production from the top 10 producer countries in the world (Data source: FAO, averaged values over the period of 1994-2017); Figure S2: Annual harvested area, production and yield of sugarcane in Brazil and USA during1961- 2017; Figure S3: Sugarcane production cycle at the Louisiana site, USA; Figure S4: Interannual variation of three vegetation indices from MODIS during 2000-2018 at the two sugarcane plantation sites. (a) Brazil site; (b) Louisiana site, USA; Figure S5: Interannual variation of climate data (air temperature, PAR and precipitation) during 2000-2018 at the two sugarcane plantation sites, derived from NCEP-DOE reanalysis S2. (a) Brazil site; (b) Louisiana site, USA; Figure S6: Interannual variation of GPP data from the MODIS MOD17A2 product during 2000-2018 at the two sugarcane plantation sites. (a) Brazil site; (b) Louisiana site, USA. Table S1: A detailed information on sugarcane planning history at the two sugarcane sites during 2000-2018; Table S2: A summary of annual precipitation, mean annual air temperature, annual PAR from NCEP Reanalysis-2 climate data, and GPP estimated from the VPM model with NCEP Reanalysis-2 climate data (GPPVPM-NCEP) during the sugarcane plant growing season at the sugarcane flux tower sites in Brazil and USA. [PERSON] and [PERSON] conceived the study. [PERSON] and [PERSON] provided in-situ data. [PERSON] did data analysis and VPM model simulation. [PERSON], [PERSON] and [PERSON] contributed to data processing, analysis and visualization. [PERSON] and [PERSON] wrote the first draft and [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] read and revised the drafts. All authors have read and agreed to the published version of the manuscript.