Factors influencing the kinetic energy of throughfall drops

The rainfall erosivity influences the detachment of soil particles, movement and washing away the surface soil layers, which affects soil degradation and leads to various environmental problems. It depends primarily on the kinetic energy of raindrops, determined by the size and velocity of raindrops. However, rainfall microstructure (size, velocity and number of raindrops) is significantly changed during the process of rainfall interception. Precipitation, that is not intercepted by the vegetation, reaches the ground as throughfall (falling directly through the gaps in the canopy or dripping from the leaves and branches) or stemflow (flowing down the branches and stem). Therefore, the kinetic energy of throughfall under the vegetation is different than kinetic energy of open rainfall.

In the urban park located in Ljubljana, Slovenia, we have monitored the rainfall microstructure in the open and underneath the deciduous (Betula pendula Roth.) and coniferous (Pinus nigra Arnold) trees between 12 July 2022 and 19 July 2023. We have analysed the differences between rainfall microstructure and kinetic energy of raindrops in the open and underneath the trees.

The observed average number of raindrops per event under both trees was lower than the number of raindrops in the open. Also, the average kinetic energy of drops per event was significantly lower under the trees than in the open. Additionally, an analysis of factors influencing the kinetic energy of throughfall drops underneath the both trees was performed using the boosted regression trees and random forest models. Both models identified rainfall amount as the most influencing factor.

Acknowledgments: Results are part of the research programme P2-0180 and research projects J2-4489, N2-0313 and J6-4628, financed by the Slovenian Research Agency (ARIS).