Seasonal variation of surface radiation and energy balances over two contrasting areas of the seasonally dry tropical forest (Caatinga) in the Brazilian semi-arid

摘要

Arid and semi-arid environments correspond to one-third of the Earth's terrestrial surface. In these environments, precipitation is an essential and limiting element for vegetation growth and ecosystem biomass productivity. The semi-arid region of Brazil comprises around 11.5% of the national territory, where the Caatinga biome originally composed similar to 76% of this area, with water deficit as a prominent feature, annual rainfall lower than 800 mm, temperatures ranging between 25 and 30 degrees C, and potential evapotranspiration higher than 2000 mm/year. Research on the dynamics of mass and heat fluxes through techniques such as eddy covariance (EC) has contributed to estimate the magnitude and seasonal patterns of turbulent exchanges between ecosystems and the atmosphere. This study was conducted in an area of dense Caatinga (DC) and another of sparse Caatinga (SC) from 2013 to 2014. It was observed that albedo (alpha) and net radiation (R-n) were higher in the SC compared with DC since the magnitude of incoming shortwave radiation was higher in this area. It was found that most of the R-n is converted to sensible heat flux (H), mainly during the dry period in the SC, about 50% for H and 20% for lambda E. The energy balance closure showed that the turbulent fluxes (H + lambda E) were underestimated in comparison to the available energy at the surface (R-n - G). We also observed that this discrepancy was higher in the DC area, corresponding to similar to 30%.