## 4 Energy Balance  
Figure 5 shows the average daily cycle of the simulated energy balance in the study area for the years 2009 and 2012. In general, the daily pattern of Rn agrees with that of solar radiation. This correspondence has been observed across different ecosystems and in regions with different climatic conditions [10; 50; 51]. Rn is negative or approaches zero during the nighttime, when radiative cooling of the surface dominates and presents positive values during the day because of the incidence of solar radiation. In general, the average daily behavior of the energy balance components (Rn, H, LE and G) agreed with the daily pattern of solar radiation in both years. The exceptions were H and LE during 2012 (Figure 5B). The maximum value of LE was reached at approximately 09:00, whereas the maximum value of H was observed around 14:00 local time. H increased continuously from 09:00 h until 14:00 h while LE decreased within the same time interval. Figure 5: Hourly cycle of the energy balance components (Wm\({}^{-2}\)) simulated during the years 2009 (**A**) and 2012 (**B**). Maximum LE occurred at 09:00 h, coinciding with the daily period when the Caatinga exhibits the maximum stomatal opening, according to [20]. After this time, also according to [20], VPD steadily increases until 14:00 h. During this time interval, Caatinga plants exert greater control over evapotranspiration by progressively reducing stomatal aperture to prevent excessive water loss [20; 21]. Consequently, most of the available energy within this period (from 09:00 to 14:00 h) is converted into H.  
The soil heat flux (G) has negative values throughout most of the day and night. Positive values are only observed between 9:00 a.m. and 5:00 p.m. (local time), reaching a maximum of 53.87 Wm\({}^{-2}\) in 2009 and 53.14 Wm\({}^{-2}\) in 2012. In 2009, the values of G were higher compared to 2012. Table 2 presents the annual and seasonal averages (dry and wet seasons) of the components of the energy balance and their respective partitions. It can be noted that the annual and seasonal averages of Rn varied little, from 163.4 to 170.2 Wm\({}^{-2}\), which is a difference of less than 5%. This small difference is due to little seasonal variation in solar radiation, the main modulator of Rn [10; 50; 51]. Such radiation behavior is typical of tropical regions, especially at low latitudes (below 10\({}^{\circ}\)). The fact that the year 2009 was rainier does not substantially alter the partition of energy fluxes compared to 2012 in this biome. As demonstrated in previous studies [4], the water use efficiency and evapotranspiration patterns respond more strongly to consecutive wet days rather than the amount of water precipitated in a given month, which can occur on isolated days. Additionally, according to Table 2, it can be observed that the energy balance closure (EBC) simulated by the SITE model showed a seasonal variation ranging from 0.58 to 0.86, with an overall average of \(\sim\)0.70 for the two years. This value is considered satisfactory, albeit lower than the values obtained experimentally using the EC method [10; 39; 52; 53]. The relatively modest closure observed with the SITE model simulations is likely associated with discrepancies between the model's results and the observed values, as reported by [34; 35]. Although these studies were conducted in different environments, they revealed a consistent pattern in the SITE simulations: an overestimation of LE and an underestimation of H. Additionally, ref. [32] also noted that, in general, the SITE model overestimates Rn and underestimates G, which theoretically implies a higher available energy compared to observed values. Studies indicate that in the Caatinga, the majority of available energy is converted into sensible heat flux during the dry season, and the partitioning of energy flux is directly associated with vegetation characteristics and changes in land use [10; 19; 23].