## 1 Introduction  
Deforestation and land use change affect the preservation of tropical forests, demanding great efforts from the scientific community to investigate and discover the main natural controls of biophysical and phenological aspects in these ecosystems. With that, it is possible to better understand their ecological functions, which in turn allows the extrapolation of in situ observations to larger areas through remote sensing data, for example. This bigger picture provides more accurate and detailed scenarios regarding the impacts of climate change and land use change on landscape and the environment. In this perspective, studies on the characterization of the biosphere-atmosphere interactions are crucial to highlight the importance of tropical forests to the global climate balance [1; 2; 3; 4]. Given the particularities and the variety of physiognomies within a single biome, these studies are also useful for the development of more accurate biosphere-atmosphere models [5; 6; 7], for the validation of remote sensing products [8; 9; 10; 11], for the characterization of vegetation response to the natural seasonality of the environment [7; 12; 13], and they can also be used as proxies in the analysis of climate change impacts and implications. In Brazil, most research in this field is concentrated in the Amazon region [14; 15; 16; 17; 18]. Thus, there is a relative scarcity of studies on the seasonality of phenological aspects of other Brazilian biomes and their atmospheric controls, or even studies regarding the validation of remote sensing data over these areas. However, recent studies indicate that other Brazilian biomes such as the Caatinga behave as efficient carbon sinks if compared to other dry forests across the globe [19]. These authors show that even in the dry season, the Caatinga uptakes from 145 to 169 gC m\({}^{-2}\) year\({}^{-1}\) due to the low respiration rates of the ecosystem. Nevertheless, there is little point-based experimental evidence apart from these results and, therefore, remote sensing estimates can be important sources of information on the ecological functions of the Caatinga, as suggested by the study by [PERSON] [20]. Although observations at a single point are not representative for the entire ecosystem, such observations are useful to improve the understanding of ecosystem productivity and gas exchange in different biomes, being a common analysis in the literature [2; 4; 19] in studies using the eddy covariance technique in a single tower, given the high cost of keeping many experiments covering the same area. Such data can serve as a subsidy for several actions, such as validating remote sensing products for larger areas. Remote sensing methods provide means to monitor carbon dioxide (CO\({}_{2}\)) exchange and several other vegetation growth parameters in almost all kinds of ecosystems, from boreal forests [21] to the different mosaic vegetation patterns of tropical forests [9]. Furthermore, they may be associated with information collected through eddy covariance systems, providing more robust measurements to characterize energy and water fluxes in ecosystems (e.g., Maselli [22]). In addition, due to limitations in establishing long-term series in these environments, measurements in shorter periods (2 years or more) are already efficient in characterizing the seasonality of local variables and validating remote sensing products [2; 3; 19; 20]. Carbons fluxes, including photosynthesis and respiration, are strongly coupled to the water cycle in the various terrestrial ecosystems [23; 24]. Water-use efficiency (WUE) is commonly defined as the ratio between gross primary production (GPP) and evapotranspiration (ET) at the ecosystem level [25], representing an important ecophysiological index relating water and carbon cycles.