Looking under the canopy: Modelling how single trees contribute to runoff reduction in cities

Abstract

Urban trees provide a wide range of ecosystem services, including urban cooling, flood control, biodiversity, and air quality improvement. However, their impact depends on their physical attributes, seasonality, placement, and distribution in urban settings. This study focuses on the role of trees in stormwater management. Using the modified Gash and Rutter formulation, we developed a spatially distributed model to simulate individual tree’s interception capacity and throughfall. The model was applied to individual trees with time varying leaf area index (LAI) under different rainfall intensity, and canopy saturation conditions. Model validation against measurements showed strong agreement for total throughfall (R² ≃ 0.83) and interception (R² ≃ 0.61). At the urban scale, applying the model to a pilot area in Copenhagen, Denmark, resulted in a total runoff reduction of 15.2%, with local contributions varying between 2% and 43% based on tree characteristics. However, tree effectiveness was primarily driven by rainfall intensity and tree seasonality. Further research is needed to refine species-specific interception capacity and improve LAI-based parameterization in tree interception. Integrating this approach with hydrodynamic simulations could enhance understanding of trees’ local flood control contributions, supporting urban planning and tree-planting strategies to optimize city resilience.