Abstract While evapotranspiration (ET) is an important component of the global water cycle, its temporal variations (ΔET) and underlying mechanisms are controversial. Based on the newest FLUXNET dataset and six ET products, we investigate ΔET for different ecosystem types during the recent two decades (1995–2014). We found an ET hiatus (decreasing in ET) at most sites (46 of 67) based on both in-situ observations and the ET products. The environmental drivers, surface conductance (Gs) and water use efficiency (WUE) are found to be responsible for ΔET. Changes in structural (by leaf area index, or LAI) and physiological (by Gs and WUE) variables contributed nearly equally to ΔET. Although Gs may impose a larger positive effect on ET than LAI, its effect may substantially offset the negative effect via WUE. Our study provides robust observational evidence that global ET stayed roughly unchanged in the past two decades. The results also highlight the importance of incorporating both vegetation structural and physiological effects in the projections of ΔET under a changing climate.

中文翻译：

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植被结构和生理控制解释的全球蒸散中断

摘要 虽然蒸散量 (ET) 是全球水循环的重要组成部分，但其时间变化 (ΔET) 和潜在机制仍存在争议。基于最新的 FLUXNET 数据集和六个 ET 产品，我们调查了最近二十年（1995-2014 年）不同生态系统类型的 ΔET。根据原位观测和 ET 产物，我们在大多数站点（67 个中的 46 个）发现了 ET 间断（ET 减少）。发现环境驱动因素、表面电导 (Gs) 和用水效率 (WUE) 是 ΔET 的原因。结构（通过叶面积指数，或 LAI）和生理（通过 Gs 和 WUE）变量的变化对 ΔET 的贡献几乎相等。尽管 Gs 可能对 ET 施加比 LAI 更大的正面影响，但它的影响可能会通过 WUE 大大抵消负面影响。我们的研究提供了强有力的观察证据，表明全球 ET 在过去二十年中大致保持不变。结果还强调了在气候变化下将植被结构和生理效应纳入 ΔET 预测的重要性。