## 1 Introduction  
With the intensification of global climate change, phenomena such as El Nino and La Nina are becoming more frequent and progressively affecting larger areas [1]. Simulations show that global climate change can adversely affect arid and semiarid regions by extending the dry period and jeopardizing the biodiversity of the ecosystem [2; 3]. Seasonally dry tropical forests (SDTF) occur widely in the world, mainly in the Americas, Central and South Africa and India. The semiarid lands of Brazil are widely dispersed throughout the North-Eastern region, covering an area of approximately 865,000 km\({}^{2}\) with the Caatinga biome as the main vegetation type [4; 5]. The Caatinga is a biodiversity-rich area [6], but its landscape is changing due to intense human activities, particularly deforestation and fires (slash-and-burn practices), with large native vegetation areas being replaced by pastures [5]. Such a process has important implications in land-use changes, and consequently in mass and heat fluxes changes in the soil-vegetation-atmosphere interface [7]. Thus, it is relevant to understand and quantify processes related to the Caatinga energy balance and carbon flux, which can be essential for the formulation of environmental and public policies. Forests are widely considered to have the largest potential to act as sinks for atmospheric CO\({}_{2}\)[8]. Several studies have shown the potential of different types of ecosystems to sequester carbon in response to the increased atmospheric CO\({}_{2}\) associated with climate change or to release CO\({}_{2}\) as a result of changes in land use and management [9; 10; 11; 12]. In Brazil, energy and CO\({}_{2}\) fluxes have been studied in biomes such as wetlands--the Pantanal [13]; Cerrado [14]; the Caatinga [15; 16], but mostly in the Amazon region [17; 18; 19; 20]. The environmental biology of the Caatinga vegetation (phenology, energetic seasonality, carbon and water fluxes) is a key component in the study of regional carbon cycle [4; 16; 21; 22] and for the understanding of the ecosystem dynamics and how environmental drivers may affect it (e.g., recovery after wildfires and land use changes).The importance of the Caatinga for the regional climate [23; 24] is therefore unquestionable [5; 25], but its vulnerability to drought and the risks associated with a drier climate [26] is uncertain, due to a lack of studies in this region. The eddy covariance technique (EC) has been widely used to determine mass and heat fluxes in the soil-vegetation-atmosphere interface. It is particularly useful to assess whether a particular ecosystem is acting as sources or sinks for atmospheric CO\({}_{2}\)[27; 28; 29]. Flux measurements also provide data for the evaluation of dynamic climate models [30]. EC is also useful to compare soil-vegetation-atmosphere transfer (SVATS models) with the observed seasonal behavior of ecosystem-atmosphere exchanges [31]. Few studies on the partitioning of the energy balance and/or carbon dioxide and water fluxes have been conducted in the Caatinga, particularly in areas of preserved or in-recovery vegetation [15; 16; 32; 33; 34], due to the complexity and cost of the field experiment installations. In this context, ecological and ecosystem models can be used as alternative methods to answer questions related to the interactions between the biosphere and the atmosphere. However, it is crucial to compare and validate the simulated data with those measured in situ in order to evaluate the simulations accuracy, and to calibrate specific parameters of the model according to the characteristics of a given ecosystem. The main challenge for the modeling of CO\({}_{2}\) and energy flux in the Caatinga is the adjustments of the site-specific biophysical and morphophysiological vegetation characteristics inherent to the different seasons of the year. For example, increasing the leaf area index (LAI), specific leaf area (SLA) and dimension of leaves may increase the rate of photosynthetic CO\({}_{2}\) fixation [9].