Benefits of an urban isolated tree combined with ground covers for stormwater management through interception–infiltration–runoff processes

Source abstract

Urban trees contribute to stormwater management through crown interception loss and root-enhanced infiltration that reduces surface runoff. However, the effects of tree crowns and roots on surface runoff are often simplified in simulation models such as the Storm Water Management Model (SWMM). This study aimed to evaluate the benefits of an urban isolated tree combined with different ground covers for stormwater management through interception–infiltration–runoff (IIR) processes using SWMM. The crown interception processes for an isolated tree (i.e., Zelkova tree, 6.4 m height) were measured for three years using a weighing lysimeter to obtain the net rainfall reaching the ground surface beneath the tree crown. Additionally, the root-influenced infiltration process was modeled using an optimal set of parameters that were validated using irrigation-drainage experiment data. By applying the set of parameters to SWMM, surface runoff reduction for different combinations of 15 rainfall events was estimated. The results revealed that the target tree reduced surface runoff by 4.6% during heavy rains. Additionally, when combined with the tree, the impermeable and water-retaining pavements achieved 65.5% and 12% reductions during the 15 rainfall events. From the estimation results of annual surface runoff in Tokyo, similar results were observed for permeable pavement with and without trees. However, the presence of trees reduced annual surface runoff by approximately 2%, 70%, and 8% compared to soil, impermeable, and water-retaining pavements alone, respectively. Trees with soil-filled pits effectively contribute to urban stormwater management when combined with impermeable and water-retaining pavements.