# WUE and CO2 Estimations by Eddy Covariance and Remote Sensing in Different Tropical Biomes
## 1 Introduction  
Discussions on climate change have become increasingly more relevant in the general scientific community, particularly since the creation of the Intergovernmental Panel on Climate Change (IPCC), which is composed of a diverse group of worldwide researchers, focusing on climate change studies and its impacts on society. Since the industrial revolution, the concentration of carbon dioxide (CO\({}_{2}\)) in the atmosphere has increased with the use of fossil fuels, deforestation, the use of nitrogen in agriculture and livestock farming, which are reported to be the main uses responsible for the anthropic greenhouse effect. Studies have already shown the relevance of biosphere-atmosphere interactions in Brazilian biomes regarding planetary climate regulation due, for example, to water, energy, and carbon exchanges with the atmosphere [1; 2; 3; 4; 5; 6]. However, there are still uncertainties regarding these processes due to the remarkable diversity of physiognomies, landscapes and other biophysical aspects that might play a role in differentiating atmospheric patterns from one place to another within each biome. To reduce these uncertainties, in situ measurements are needed to better understand the particularities of each environment. Furthermore, these observed data can also be used to assess soil-vegetation-atmosphere models [7; 8; 9; 10] and to analyze satellite-derived estimates of water and/or CO\({}_{2}\) balance components [11; 12; 13; 14; 15; 16]. Both these models and remote sensing data are extremely important in providing reliable information on CO\({}_{2}\) exchanges over tropical forests where flux tower coverage is scarce or non-existent, such as in many parts of Brazil. Additionally, certain forest physiognomies are not endemic to Brazil, but occur in several other regions of the globe, and therefore, their particularities regarding biophysical patterns need to be understood in detail. Wetlands in tropical rainforests such as the Amazon are environments where organic production rates are high and anoxic conditions are frequent, and therefore, they represent crucial zones for the global balance of greenhouse gases in the atmosphere. Cerrado ecosystems (savannas), however, are located at the tropics and subtropics and are characterized by marked wet and dry seasons. They cover approximately 60%, 50% and 45% of the total area of Africa, Australia and South America, respectively [17]. These ecosystems play an important role in the cycle of several greenhouse gasses, as reported by the studies [18; 19; 20] among others, and on energy fluxes (latent and sensible heat) in the context of climate change, since they cover approximately 20% (2.7 billion ha) of the global surface [17]. Carbon dynamics and biophysical evapotranspiration controls over tropical Brazilian ecosystems and in other regions of the world have also been studied because of the need to better understand the effects of land use change on regional and global biogeochemical cycles [13; 15; 21]. Evidently, it also allows us to estimate the contribution of tropical biomes to the regional and global climate controls, also comprising the relationship between precipitation, evapotranspiration, plant productivity and greenhouse gas exchanges within the atmosphere [22]. These changes motivated the development of various research fields within climate sciences focusing on the debate over greenhouse gases cycles and anthropic influence over these cycles. CO\({}_{2}\) concentration in the atmosphere surpassed 405 ppm [23] and continues increasing each decade, as well as that of other greenhouse gases. Therefore, it is necessary to develop methods and techniques to quantify these emissions and the fluxes of these gases, improving the understanding on how different environments function and respond to land-use changes. The eddy covariance method (EC) directly and non-intrusively estimates the vertical transport of CO\({}_{2}\) and other greenhouse gases.