Evapotranspiration (ET) is the main driver of the energy balance partitioning and influences hydrological and carbon cycles at global, regional and local scales. Furthermore, it is the main requirement for developing strategies to improve water use in agriculture. It is known that there is a close relationship between ET and rainfall, especially in tropical environments. Thus, the main goal of this article was to evaluate how ET and its controls (surface conductance - Gs; decoupling coefficient - Ω; Priestley-Taylor parameter - α) respond to the seasonal variability of meteorological forcing in tropical grazed pastures under the climatic conditions of Northeast Brazil. ET was measured using an Eddy covariance (EC) system and analyzed based on data from two agricultural years (2015–2016 and 2016–2017) with negative (-59 mm) and positive (356 mm) rainfall anomaly, respectively. ET exhibited pronounced seasonality, closely aligned with the seasonality of rainfall. Lower daily averages were observed during the dry season in both agricultural years (1.01 ± 0.60 and 0.89 ± 0.44 mm, respectively). On the other hand, higher daily averages were observed during the rainy season (2.44 ± 0.75 and 4.83 ± 0.96 mm, respectively). The Gs patterns and the significant correlation between Gs, Ω, and α (p < 0.01) indicate that surface control prevails over atmospheric control on an annual scale. This finding is confirmed by the annual mean values of Ω (0.27, 2015–2016) and α (0.38, 2016–2017). This relationship is likely induced by a vegetative stomatal control mechanism, which protects the vegetation against excessive water loss during periods of high temperatures and low humidity levels. These findings are crucial for understanding how droughts modulate components of the energy balance and water fluxes in pastures, especially given the intensification of these events. This has implications for the implementation of climate change mitigation policies and soil management.

中文翻译：

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雨养条件下热带牧场蒸散量的气象和生物物理控制


蒸散量（ET）是能量平衡分配的主要驱动力，影响全球、区域和地方尺度的水文和碳循环。此外，这是制定改善农业用水战略的主要要求。众所周知，ET 与降雨量之间存在密切关系，特别是在热带环境中。因此，本文的主要目标是评估 ET 及其控制（表面电导 - Gs；解耦系数 - Ω；Priestley-Taylor 参数 - α）如何响应气候条件下热带牧场气象强迫的季节性变化巴西东北部。使用涡协方差（EC）系统测量ET，并根据两个农业年份（2015-2016年和2016-2017年）的数据进行分析，分别为负（-59毫米）和正（356毫米）降雨距平。 ET 表现出明显的季节性，与降雨的季节性密切相关。两个农业年份的旱季日平均值均较低（分别为 1.01 ± 0.60 和 0.89 ± 0.44 毫米）。另一方面，雨季期间的日平均值较高（分别为 2.44 ± 0.75 和 4.83 ± 0.96 毫米）。 Gs 模式以及 Gs、Ω 和 α 之间的显着相关性 (p < 0.01) 表明，在年尺度上，地表控制优于大气控制。 Ω（2015-2016 年为 0.27）和 α（2016-2017 年为 0.38）的年平均值证实了这一发现。这种关系可能是由植物气孔控制机制引起的，该机制可以保护植被在高温和低湿度期间免受过度失水。 这些发现对于了解干旱如何调节牧场能量平衡和水通量的组成部分至关重要，特别是考虑到这些事件的加剧。这对减缓气候变化政策和土壤管理的实施具有影响。