Assessing rainfall-runoff processes of an urban isolated tree combined with different pavement types using a field-measured and simulation-calibrated model

Isolated tree and permeable pavements are typical units for urban green infrastructure that contribute to stormwater management during rainy days through crown interception loss and enhancing infiltration by tree roots and permeable materials. Some rainwater is stored in tree crown, tree pits, and pavements, functioning as blue-green infrastructure for mitigating urban heat island on sunny days after rainfall. However, the interception and infiltration processes of isolated tree are simplified in the Storm Water Management Model (SWMM), potentially affecting the evaluation of synergistic benefits for tree and pavements. This study develops a field-measured and simulation-calibrated model to analyze the crown interception and root-influenced infiltration processes, aiming to assess surface runoff reduction and rainwater storage for an isolated tree combined with different pavement types. The crown interception processes were measured using a weighing lysimeter, revealing an interception loss of 11.2% of the target tree during 15 rainfall events. Meanwhile, the net rainfall (i.e., the rainfall amount reaching the ground surface beneath tree crown) variations were also obtained for rainfall-runoff analysis considering crown interception. Additionally, the root-influenced infiltration process was represented by an optimal set of parameters that was determined by parameter optimization and validated using experimental results from two irrigation-drainage events. The coefficient of determination (R²) between simulated and measured drainage and storage exceeded 0.9. According to the developed model, the rainfall-runoff processes of the target tree combined with impermeable, permeable, and water-retaining pavements during 15 rainfall events were analyzed. Surface runoff reduction and rainwater storage for different combinations were quantified, providing co-design recommendations for green, blue, and brown spaces in urban areas.