## 3 Results  
### Seasonal Dynamics of Climate, Vegetation Indices, Carbon, and Energy Fluxes  
Figure 2 shows the mean monthly accumulated evapotranspiration, vapor pressure deficit (Figure 2a), and air temperature and relative humidity averages (Figure 2b), as well as monthly accumulated rainfall. Evapotranspiration, relative humidity of the air, and rainfall are inversely related to VPD and air temperature, which peaked during the dry season of 2015 (29.8 \({}^{\circ}\)C, Figure 2b). Air temperature varied 11% between monthly minimum and maximum values, while relative humidity varied more sharply, roughly 40% between minimum and maximum values. ET was higher in April (94.4 \(\pm\) 8.5 kg H2O m\({}^{-2}\) month\({}^{-1}\)), coinciding with the highest rainfall values. Mean ET during the wet season was 280.9 \(\pm\) 23.9 kg H2O m\({}^{-2}\), which is 225% higher than in the dry season (86.4 \(\pm\) 8.4 kg H2O m\({}^{-2}\)). At the annual scale, mean VPD in 2015 was 2.6 kPa while in 2014, it was 2.2 kPa, which may be explained by the slightly lower precipitation (513 and 466.5  mm in 2014 and 2015, respectively) and higher air temperature, with a consequent decrease in relative humidity of the air between these years (Table 1). In the wet season, 83% of mean annual rainfall occurred, which accounted for 53 days in which rainfall occurred in 2014 and 26 days in 2015.  
The seasonal dynamics of the vegetation indices (EVI and NDVI) show the pattern of surface phenology regarding canopy structure and the development of the vegetated area (Figure 3a). We can observe that the seasonality of vegetation is directly related to local precipitation patterns (Figure 2). The NDVI and EVI presented higher values at the peak of the wet season (NDVI > 0.6; EVI > 0.4), subsequently reducing in magnitude with the establishment of the dry season, reaching NDVI < 0.4 and EVI < 0.2 and indicating the beginning of leaf senescence in the Caatinga. The occasional occurrence of rainfall events in the dry-wet transition season were sufficient to increase vegetation activity in November 2014 (NDVI > 0.5; EVI > 0.3), which led to an increase in latent heat flux, suggesting that the onset of the wet season exerts a strong control in the production of biomass in this ecosystem. These data are strongly related to energy fluxes, with higher NDVI and EVI values occurring in the wet season when evapotranspiration (and LE) is also higher (Figure 3b).  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Variable** & **2014** & **2015** \\ \hline \hline \multicolumn{1}{l}{Tair (\({}^{\circ}\)C)} & \(27.8\pm 3.8\) & \(28.4\pm 4.1\) \\ \multicolumn{1}{l}{RH (\%)} & \(54.8\pm 17.9\) & \(48.9\pm 17.1\) \\ \multicolumn{1}{l}{VPD (kPa)} & \(2.2\pm 1.18\) & \(2.6\pm 1.20\) \\ \multicolumn{1}{l}{ET (kg H\({}_{2}\)O m\({}^{-2}\) day\({}^{-1}\))} & \(1.2\pm 1.05\) & \(0.8\pm 0.93\) \\ \multicolumn{1}{l}{Rainfall (mm)} & 513 & 466.5 \\ \multicolumn{1}{l}{Rn (W m\({}^{-2}\))} & \(161.0\pm 219.9\) & \(160.3\pm 220.2\) \\ \multicolumn{1}{l}{H (W m\({}^{-2}\))} & \(83.9\pm 142.0\) & \(93.2\pm 152.2\) \\ \multicolumn{1}{l}{LE (W m\({}^{-2}\))} & \(35.5\pm 66.7\) & \(25.5\pm 56.6\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Annual average and standard deviation of climate and energy flux variables measured during 2014 and 2015. Rainfall refers to accumulated values.  
Figure 2: Interannual variability of the monthly: (**a**) accumulated evapotranspiration (ET) and vapor pressure deficit (VPD) average; (**b**) air temperature (Tair) and relative humidity (RH) averages. The monthly accumulated rainfall (yy/mm/dd) is presented in both panels as grey bars.  
Net radiation peaked at roughly 200 W m\({}^{-2}\) day\({}^{-1}\) in November. Sensible heat flux accounts for most of the energy balance partitioning during the dry season, while latent heat flux is superior during the wet season. Table 1 shows the mean and deviation of the studied variables in each experiment year.