# WUE and CO2 Estimations by Eddy Covariance and Remote Sensing in Different Tropical Biomes
## 3 Results
### Carbon Fluxes and Wile  
According to the daily GPP analysis shown in Figure 7, seasonal changes in GPP are more intense in the Caatinga and Pantanal sites if compared to the Amazonia and Cerrado sites. The coefficient of determination (R\({}^{2}\)) between observed GPP and evapotranspiration (Figure 8) was also higher in the Caatinga and Pantanal. Maximum values reach up to 9.0 gC m\({}^{-2}\) d\({}^{-1}\) in the Cerrado and Amazonia, while the lowest GPP values reach approximately 0.5 gC m\({}^{-2}\) d\({}^{-1}\) in the Caatinga. The seasonality and intensity of GPP values in the Amazon and Cerrado are similar, while in the Caatinga and Pantanal, they are similar only between June and July. Regarding maximum values, GPP peaks in April in the Cerrado, coinciding  
Figure 6: Hourly and monthly variation of energy fluxes: (**A**) net radiation (Rn, W m\({}^{-2}\)), (**B**) latent heat flux (LE, W m\({}^{-2}\)) and (**C**) sensible heat flux (H, W m\({}^{-2}\)). with the period of least radiation availability after the site inundation, while in the Amazon, GPP peaks in October, characterized by high radiation, air temperature and an increase in precipitation after an annual minimum in September. We also assessed observed GPP data by comparing them with MODIS satellite data on a monthly scale (Figure 9). Results show a high overestimation of satellite data in drier periods, especially in the Amazonia site (Figure 9A). In the Caatinga site (Figure 9B), measurements are more similar from September to November if we consider the median values and monthly variability. In the Cerrado site (Figure 9C), MODIS GPP underestimates observed data in the dry season (August and September), while in the Pantanal (Figure 9D), daily variability of MODIS data is much more prominent than observed data, despite the coherence in representing the seasonal cycle. Given these patterns, the best correlations were found in the Pantanal (R\({}^{2}\) = 0.31) and Caatinga (R\({}^{2}\) = 0.27) sites (Figure 10), with values similar to what is found in the general literature regarding MODIS GPP assessment (Table 1). Due to the importance of investigating specific local water cycles and the effect of drought on the water balance and carbon uptake, we calculated WUE (Figure 11), showing interesting variability aspects depending on the studied biome. WUE is lower in the site  
Figure 8: Correlation between daily GPP averages and evapotranspiration for each site. The size of the circles indicates the intensity of water-use efficiency (WUE) estimated at each day (gC kg H\({}_{2}\)O day\({}^{-1}\)). Figure 7: Monthly GPP (gC m\({}^{-2}\) day\({}^{-1}\)) boxplot for each site and study period (Amazonia: 2009\(-\)2011; Caatinga: January 2014\(-\)July 2015; Cerrado: 2004\(-\)2006; Pantanal: 2015\(-\)2016). with the highest evapotranspiration (Pantanal), while a remarkable variability and the highest WUE values are found in the Caatinga site. WUE in the other sites did not present great seasonal differences, with values reaching approximately 4.0 gC kg H\({}_{2}\)O day\({}^{-1}\) in the driest months (between September and October). WUE surpassed 15 gC kg H\({}_{2}\)O day\({}^{-1}\) in the driest month (September) of the driest site (Caatinga), sharply decreasing in October with the occurrence of rainfall. Mean annual WUE values estimated in this study delineate new thresholds if compared to previously reported values in the literature (Table 2), with the Pantanal site featuring WUE lower than 1.0 gC kg H\({}_{2}\)O year\({}^{-1}\) and the Caatinga site featuring values near 5.8 gC kg H\({}_{2}\)O year\({}^{-1}\), which is much higher than in other dry forests studied in the literature. Figure 10: Correlation between daily tower GPP \(\times\) MODIS GPP for each site. The size of the circles indicates the intensity of daily accumulated rainfall (mm).