Partitioning of evaporation into interception and transpiration for the overstory, understory, and forest floor in a coniferous forest in the Netherlands

Forests play a significant role in altering precipitation patterns by interception and transpiration. Interception causes a redistribution and (mostly) a reduction of the plant available water, which has direct feedback on the transpiration. Additionally, most forests have an overstory, an understory, and a forest floor, which makes this feedback mechanism even more complex to unravel. In this study we aim to partition total evaporation into interception and transpiration for the overstory, understory, and forest floor for a coniferous forest in The Netherlands.

At the Ruisdael Observatory Loobos, an eddy covariance system on top of a 38-meter-high tower measures total evaporation of the forest. Along this tower, vapour pressure deficit is probed at 11 different heights. Net radiation is measured at ground level and the top of the tower. By applying the Bowen Ratio Energy Balance - method (BREB) between the different sensors, we can partition the total evaporation flux above and below the overstory. Additionally, fiber optic cables are installed along the tower, where one cable measures the air temperature over the height and another cable, which has a wet cloth, the wet bulb temperature. By applying BREB, the fiber optic cables will provide a near-continuous total evaporation profile from the forest floor to far above the canopy. To partition evaporation into interception and transpiration, we will make use of leaf wetness sensors by assuming that transpiration only occurs when the leaves or needles are dry. To verify this assumption, we also installed a rain gauge above the canopy and several gauges below to measure throughfall.

Having multiple instruments to measure the different evaporation components, allows us to partition total evaporation into interception and transpiration for the different layers and cross-validate it. This poster combines previous experimental research into an integrated approach. The set-up is outlined and first results using data from the summer of 2023 and spring of 2024 are presented.