## 2 Materials and Methods
### Micrometeorological Measurements and Application of the SITE (Simple Tropical Ecosystem) Model  
The procedure for calculating hourly NEE values can be found in [21; 38]. The CO\({}_{2}\) flux calculation involved a series of procedures that included: coordinate rotation correction using the planar fit method, sonic virtual temperature correction, corrections for density fluctuation (WPL-correction), and frequency response correction. After the calculations, a robust quality control and filtering process was performed to detect and exclude spikes and physically inconsistent data. Subsequently, gap-filling was performed. A detailed description of the complete methodology is described in previous research: [10; 20; 21; 39]. The partitioning of CO\({}_{2}\) fluxes was performed using the algorithm reported in [40], which uses the nighttime period to divide NEE into Reco and GPP. During the night, GPP is assumed to be zero, and therefore, NEE is equal to Reco. The nighttime fluxes were adjusted with respect to air temperature through the [PERSON] and [PERSON] equation [41]. In both the filtering and gap-filling procedures, we used an online tool from the Max Plank institute--[[https://www.bgc-jena.mpg.de/REddyProc/ui/REddyProc.php](https://www.bgc-jena.mpg.de/REddyProc/ui/REddyProc.php)]([https://www.bgc-jena.mpg.de/REddyProc/ui/REddyProc.php](https://www.bgc-jena.mpg.de/REddyProc/ui/REddyProc.php)), accessed on 25 March 2022. The energy balance, Rn and G, were directly measured, while LE and H were determined using high-frequency data measured by the EC system as described by [10; 39]. Micrometeorological data measured at the tower, located 11 m above the surface, were used as input data SITE simulations. Observations included air temperature, rainfall, horizontal wind speed, downward shortwave and longwave radiation, and specific humidity. The model was calibrated and validated for the study region considering the years 2014 and 2015 [32]. Energy balance data (Rn, LE, H, and G) were used, where Rn represents the radiation balance, H denotes the sensible heat flux (heating of the air near the surface), LE corresponds to the latent heat flux (evaporation of water from the soil and transpiration of plants), and G represents the heat flux in the soil (heating of the soil). The carbon balance (GPP, Reco, and NEE) was obtained using the EC method during two consecutive years (2014 and 2015) in the ESEC-Serido. For model calibration, ref. [32] adopted the sequential method, selecting parameters with the highest probability of influencing the model's outcome. These parameters include the initial soil moisture fraction (\(\theta\)g/\(\theta\)d), stomatal conductance coefficient (m), maximum capacity of the Rubisco enzyme (Vmax), typical dimension of leaves (du), typical dimension of stems (ds), leaf width (w), and specific leaf area (SL), based on previous sensitivity analyses [34; 42]. Table 1 presents the calibration parameters used for the Caatinga biome by [32]. The performance of the model was evaluated and analyzed using Taylor diagrams, which display the Pearson correlation coefficient (r), standard deviations (SD) between the observations and simulated data, and root mean square error (RMSE). Additionally, the model's performance was assessed using the following statistical measures: median absolute error (MAE) and Willmott's index of agreement (d). Further details regarding the model validation can be found in [32]. The SITE model was used to compute a multi-year series of the energy and CO\({}_{2}\) balance of a Caatinga area within the ESEC-Serido. In the present study, the model input data consisted of meteorological data observed in 2009 (1019.6 mm of rainfall), considered a wet year compared to the region's climatology which has an annual average below 800 mm, and in 2012 (198.2 mm of rainfall) was characterized as a year with extremely low rainfall. These measurements were obtained from an automatic weather station belonging to the INMET (National Institute of Meteorology) network.