Observations of canopy storage capacity and wet canopy evaporation in a humid boreal forest

Abstract

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-m 2 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.

Long-term soil water content dynamics under different land uses in a small agricultural catchment

“…Canopy storage capacity is a major part of the water balance. Ochoa-Sánchez et al (2018) found that canopy storage of an Andean grassland can be around 2 mm, which is similar to tree canopy water storage determined by Hadiwijaya et al (2021). Most studies in current literature show that the greatest relative throughfall among land use types can be obtained in forests while the greatest stemflow, when the rainwater drips from the stems, occurs in grasslands (Sadeghi et al, 2020).…”

Sensitivity Analysis of the Maximum Entropy Production Method to Model Evaporation in Boreal and Temperate Forests

“…The same can be said of the use of a water stress factor η s set at a constant value of 1 (Table ). Peak evaporation was underestimated which could be due to the fact that interception was not simulated in the current implementation of the MEP model although it can amount to ≈20% of evaporation in boreal forests (Grelle et al., 1997; Hadiwijaya et al., 2021; Pomeroy et al., 1999). Evaporation early in the growing season was often overestimated, notably at deciduous temperate forest sites (Figures 1a–1c).…”

Seasonal dynamics of canopy interception loss within a deciduous and a coniferous forest

“…For the first approach, data for precipitation events fulfilling the following four requirements are used: (1) the duration of the event was more than 4 h, (2) the total precipitation exceeded 5 mm, (3) the canopy was dry prior to the event (no precipitation for 8 or 18 h if the previous event ended before midday or after midday, respectively), and (4) the duration of breaks in the rainfall during the event was no more than 2 h (similar procedure as presented by Hadiwijaya et al, 2020;Pypker et al, 2012). For the second approach, a precipitation event is defined as observed rainfall greater than 0.5 mm of rain, and no rain has fallen minimum 6 h prior to the beginning of the event (the same procedure as presented by Link et al, 2004).…”

“…Forest evapotranspiration includes transpiration by the vegetation, evaporation from the soil and interception loss. Studies on canopy interception loss have been completed in a variety of forest types and climates; humid tropical rainforest (Asdak et al, 1998;Jetten, 1996;Lloyd et al, 1988), semi-arid coniferous forest (Motahari et al, 2013), Mediterranean deciduous and coniferous forest (Llorens & Domingo, 2007), temperate deciduous (Herbst et al, 2008;Hörmann et al, 1996) and temperate coniferous forests (Cisneros Vaca et al, 2018;Hadiwijaya et al, 2020;Klaassen et al, 1998;Link et al, 2004;Pypker et al, 2005;Ringgaard et al, 2014). Globally, forest interception is highly variable in time and space and can comprise a substantial evaporative loss (Gerrits et al, 2010;Klaassen et al, 1998;Pypker et al, 2012) and rates up to 60% of precipitation in temperate regions have been reported in extreme cases (Staudt et al, 2011).…”