Evaporation of intercepted rain by a canopy is an important component of evapotranspiration, particularly in the humid boreal forest, which is subject to frequent precipitation and where conifers have a large surface water storage capacity. Unfortunately, our knowledge of interception processes for this type of environment is limited by the many challenges associated with experimental monitoring of the canopy water balance. The objective of this study is to observe and estimate canopy storage capacity and wet canopy evaporation at the sub‐daily and seasonal time scales in a humid boreal forest. This study relies on field‐based estimates of rainfall interception and evapotranspiration partitioning at the Montmorency Forest, Québec, Canada (mean annual precipitation: 1600 mm, mean annual evapotranspiration: 550 mm), in two balsam fir‐white birch forest stands. Evapotranspiration was monitored using eddy covariance sensors and sap flow systems, whereas rainfall interception was measured using 12 sets of throughfall and six stemflow collectors randomly placed inside six 400‐m² plots. Changes in the amount of water stored on the canopy were also directly monitored using the stem compression method. The amount of water intercepted by the forest canopy was 11 ± 5% of the total rainfall during the snow‐free (5 July–18 October) measurement periods of 2017 and 2018. The maximum canopy storage estimated from rainfall interception measurements was on average 1.6 ± 0.7 mm, though a higher value was found using the stem compression method (2.2 ± 1.6 mm). Taking the average of the two forest stands studied, evaporation of intercepted water represented 21 ± 8% of evapotranspiration, while the contribution of transpiration and understory evapotranspiration was 36 ± 9% and 18 ± 8%. The observations of each of the evapotranspiration terms underestimated the total evapotranspiration observed, so that 26 ± 12% of it was not attributed. These results highlight the importance to account for the evaporation of rain intercepted by humid boreal forests in hydrological models.

中文翻译：

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湿润北方森林冠层储水量和湿冠层蒸发的观察

冠层截留的降雨蒸发是蒸散的重要组成部分，尤其是在潮湿的北方森林中，因为该地区降雨频繁，针叶树的地表蓄水能力强。不幸的是，我们对此类环境的拦截过程的知识受到与冠层水平衡的实验监控相关的许多挑战的限制。这项研究的目的是在潮湿的北方森林中，在亚日尺度和季节尺度上观察和估计冠层的储水量和湿冠层的蒸发。这项研究基于加拿大魁北克省蒙莫朗西森林的降雨截留和蒸散分区的现场估算（平均年降水量：1600 mm，平均年蒸散量：550 mm），在两个苦瓜冷杉白桦林林分中。蒸发蒸腾通过涡流协方差传感器和树汁流动系统进行监测，而降雨截留则通过随机分布在六个400-m范围内的12套通流和六个干流收集器进行测量²情节。还可以使用茎杆压缩方法直接监测存储在冠层中的水量变化。在2017年和2018年的无雪（7月5日至10月18日）测量期间，林冠层截留的水量为总降雨量的11±5％。根据雨量截获测量得出的最大冠层储存量平均为1.6 ±0.7 mm，尽管使用杆压缩方法发现的值更高（2.2±1.6 mm）。取研究的两个林分的平均值，截留水的蒸发量代表蒸散量的21±8％，而蒸腾作用和林下蒸散量的贡献分别为36±9％和18±8％。每个蒸散项的观测值都低估了观测到的总蒸散量，因此没有将其归因于26±12％。