Energy balance and surface decoupling factor of a pasture in the Brazilian Cerrado

The production of beef, soy, and corn in Brazil is currently higher in the Cerrado biome than other biomes, such as Amazon forest. The expansion of agricultural production has caused significant changes in local albedo and surface energy fluxes. Analyzing energy fluxes is essential for understanding the microclimate dynamics in the region. However, these factors are incompletely understood because of the limited number of micrometeorological measurements in the region. This study evaluated the energy fluxes and decoupling factor in pasture lands in the Brazilian Cerrado. The study was carried out in two hydrological years (2016-2017 and 2017-2018) in Tres Lagoas, Mato Grosso do Sul, Brazil. An eddy covariance system outfitted with net radiation and ground heat flux plates was used to determinate the energy balance components. There was a predominance of latent heat flux (LE) compared to the sensible heat flux in the wet season in both years. The ratio of LE to net radiation decreased significantly in the dry season, especially in 2017-2018 where high daily average Bowen ratio was found to be 3.7 (+/- 3.0). In addition, the observed surface decoupling factor (Omega), that indicates the stomata control due to atmospheric condition, was lower during the dry season, especially in 2017-2018 with an average Omega of 0.4 (+/- 0.1), and confirmed that pasture lands were highly coupled to the atmosphere during dry season. The lower annual average of Omega in 2017-2018 was mainly due to the control of stomatal conductance to maintain essential metabolic activities and plant senescence during the unexpected drought that occurred in that period. Thus, the present study shows important findings necessary to understanding how droughts modulate the energy balance components in pasture lands, mainly considering the intensification of droughts in connection with climate change.