This study analyzes the effect of shrub encroachment on actual evapotranspiration (ETa), a still poorly studied phenomenon in the Alps. The effect of shrub encroachment is investigated on an Alpine grassland in Western Italy using both data and a soil hydrological model (Hydrus 1D), which is used to model three different land covers: grassland, shrubland, and a mixture of the two land covers with a novel double vegetation approach recently introduced. Four growing seasons of eddy covariance measurements are used as an approximate reference for the interpretation and consistency of the model outputs. Also, the impact of meteorological inter-annual variability and of different environmental conditions on both modeled and measured evapotranspiration is analyzed. The modeling results show that the model is able to capture the inter-annual variability of ETa. The double vegetation approach suggests that the percentage of total transpiration flux assigned to the shrubland is between 20 and 60 %. Single-vegetation simulations show that shrubs lead to an enhancement of ETa equal to + 27.1 %, +26.0 %, +26.8 %, and + 23.9 % (range 2014–2017) compared to grassland, which could lead to an alteration of the hydrological cycle. Moreover, chambers measurements of shrubs transpiration show a good agreement with the eddy covariance measurement, suggesting that the ecosystem’s behavior is already close to a shrubland, which yields an increased ETa if compared to grassland. The evaporative index from the modeled shrubland is higher (range +24–27 %) than the case of a modeled grassland.

中文翻译：

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意大利阿尔卑斯山废弃草地的蒸散量：模拟灌木侵占的影响


本研究分析了灌木侵占对实际蒸散量 (ETa) 的影响，这是阿尔卑斯山的一个尚未得到充分研究的现象。使用数据和土壤水文模型 (Hydrus 1D) 研究了意大利西部高山草原上灌木侵占的影响，该模型用于模拟三种不同的土地覆盖：草地、灌木丛以及两种土地覆盖的混合最近推出了一种新颖的双植被方法。涡度协方差测量的四个生长季节用作模型输出的解释和一致性的近似参考。此外，还分析了气象年际变化和不同环境条件对模拟和测量蒸散量的影响。建模结果表明该模型能够捕捉ETa的年际变化。双植被方法表明分配给灌木丛的总蒸腾通量的百分比在 20% 到 60% 之间。单一植被模拟表明，与草地相比，灌木导致 ETa 增加 + 27.1％、+26.0％、+26.8％和 +23.9％（2014-2017 年范围），这可能导致水文的改变循环。此外，灌木蒸腾作用的室测量结果与涡度协方差测量结果非常一致，这表明生态系统的行为已经接近灌木丛，与草地相比，灌木丛产生的 ETa 更高。模拟灌木丛的蒸发指数比模拟草地的蒸发指数更高（范围 +24–27%）。