Análise de parâmetros biofísicos que controlam o fluxo de calor latente em área de Cerrado Campo Sujo

Abstract

The tropical savanna (locally known as Cerrado) comprises 24 % of the national territory in Brazil and is characterized by high climatic variability, particularly related to rainfall. However, the patterns of energy exchange are still poorly understood, especially in the Campo Sujo Cerrado. Therefore, this work was conducted to evaluate how biophysical parameters seasonally control the exchange of water vapor between the vegetated surface and the atmosphere of Cerrado Campo Sujo. The study was conducted at the Fazenda Miranda, located 15 km southwest of Cuiabá (15 ° 43 ' S and 56 º 04' W), where a micrometeorological tower equipped with an eddy covariance system was installed. The results for the period between March 2011 and December 2012 indicate that seasonal changes in precipitation and/or surface water availability were the most important variables in the control of energy flux and canopy conductance. During the dry season, low values of the decoupling factor indicated that the stomatal conductance was the determinant for canopy conductance. Canopy conductance, the density of latent heat flux, and the decoupling factor showed rapid and dynamic responses to pulses of rain that were qualitatively similar to those observed in arid and semi-arid ecosystems, especially when the rain event occurred during the dry season. The results obtained with a path analysis model indicated that radiation, temperature, vapor pressure deficit and soil moisture significantly affected directly or indirectly the temporal variation in canopy conductance and latent heat flux. However, to quantify the sensitivity of canopy conductance to microclimate variations and availability of water, a more sophisticated model was needed, and for this case we used the " Jarvis -Type " model, which was calibrated and validated for the study area, with a great performance (Willmott agreement index equal to 0.9856). The characterization of climatological variables, coupled with an understanding how these biophysically control the latent heat flux and the ability to successfully employ the " Jarvis -Type " model, it is now possible to perform estimates of canopy conductance considering future scenarios related to global climate change. The results of this study are an important contribution to the region of Baixada Cuiabana, since this location has some special features related to their soils, such as low moisture retention and reduced effective depth that differ much from other regions of the Cerrado of Brazil. Furthermore, the region of Baixada Cuiabana is directly responsible for the hydrological dynamics of the North Pantanal of Mato Grosso, thus, understanding controls on water vapor exchange is important for understanding hydrological variations of the North Pantanal. Therefore, tools that enable the understanding of relations between the biosphere and the atmosphere in the Baixada Cuiabana, as presented in this study, are key to understanding the consequences of the impacts on the environment caused by human activity and can provide scientific information to help inform public policies.