Academic Unit of Atmospheric Sciences, Federal University of Campina Grande, Campina Grande, Paraíba, 58109-970, Brazil.
National Institute for Space Research, São José dos Campos, São Paulo, Brazil.
Environ Monit Assess. 2020 Jul 16;192(8):524. doi: 10.1007/s10661-020-08484-y.
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 ~ 76% of this area, with water deficit as a prominent feature, annual rainfall lower than 800 mm, temperatures ranging between 25 and 30 °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 (α) and net radiation (R) 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 is converted to sensible heat flux (H), mainly during the dry period in the SC, about 50% for H and 20% for λE. The energy balance closure showed that the turbulent fluxes (H + λE) were underestimated in comparison to the available energy at the surface (R - G). We also observed that this discrepancy was higher in the DC area, corresponding to ~ 30%.
干旱和半干旱环境占地球陆地表面的三分之一。在这些环境中，降水是植被生长和生态系统生物量生产力的必要和限制因素。巴西的半干旱地区约占该国领土的 11.5%，其中原本由约 76%的凯廷加生物群落组成，这里以缺水为突出特征，年降雨量低于 800 毫米，温度在 25 到 30 摄氏度之间，潜在蒸散量高于 2000 毫米/年。通过涡度相关（EC）等技术研究质量和热量通量的动态变化，有助于估计生态系统与大气之间湍流通量的大小和季节变化模式。本研究于 2013 年至 2014 年在密集的凯廷加（DC）和稀疏的凯廷加（SC）地区进行。结果表明，与 DC 相比，SC 的反照率（α）和净辐射（R）更高，因为该地区的入射短波辐射更大。结果发现，大部分 R 转化为感热通量（H），主要是在 SC 的干燥期，H 约占 50%，λE 约占 20%。能量平衡闭合表明，与表面可用能量（R - G）相比，湍流通量（H + λE）被低估了。我们还观察到，在 DC 地区，这种差异更高，约为 30%。
