The influence of changes in leaf inclination angle and leaf traits during the rainfall interception process

Abstract

Rainfall interception is a dynamic process where raindrops exert a force on leaf surfaces causing splashing and changes in leaf inclination angles. Leaf biomechanical properties determine the resistance to changes in leaf inclination angle due to raindrop impacts. The hydrophobicity of leaf surfaces may influence water movement off the leaf. A laboratory experiment incorporating a raindrop generator and high-speed video camera was used to examine the relationships between raindrop impact, leaf biomechanics, and water droplet retention of three tree species (Acer saccharinum, Ulmus pumila, and Quercus gambelii). Specifically, we explored if the impact of a falling raindrop resulted in the maximum leaf inclination angle exceeding the water droplet retention angle, allowing for the leaf to shed the intercepted raindrop. This study found that changes in leaf inclination angle after a single raindrop impact could explain water movement off more than 6.7% of the leaf surfaces associated with the three tree species. The change in leaf inclination angle over time produced a decaying sinusoidal curve after raindrop impact. The amplitude of the change in leaf inclination angle was greater with larger drops; however, this change varied with species. Quercus gambelii was least affected by drop impact compared with Acer saccharinum and Ulmus pumila. For species with stiff leaves, such as Quercus gambelii, the resistance of movement after raindrop impact could be a factor in inhibiting the amount of precipitation shed from the canopy. The influence of raindrop impact during rainfall events and leaf biomechanical properties may inform and enhance modeling of the dynamic process of rainfall interception.