Quantifying the rainfall-partitioning process of an urban isolated tree during different rainfall events for stormwater management

Rainwater stored by trees on rainy days reduces surface runoff under heavy rainfall events and positively affects the microclimate by evapotranspiration on subsequent sunny days. However, the rainfall-partitioning process for an isolated tree, a typical urban greenery unit, remains unclear during different rainfall events. Therefore, this study quantified the rainfall-partitioning process for an isolated tree, Zelkova serrata (6.4 m height), using a weighing lysimeter. We selected 15 rainfall events with different rainfall durations and intensities over three years for analysis. The calculation results of rainfall partitioning by the crown and trunk showed that stemflow was positively correlated with rainfall intensity, and the staying interception (crown storage) was related to the maximum crown storage capacity, which was 3.61 and 9.19 L in 2010 and 2012, respectively. The effect of leaf area index (LAI) on throughfall was not evident because of the small difference in LAI between 2010 and 2012. Additionally, the simulation results of rainfall partitioning by the tree-soil system revealed five of the 15 rainfall events with surface runoff potential. Moreover, the interception loss, interception rate, and rainfall loss estimated based on the analysis results were 11.2%, 12.0%, and 9.6%, respectively. The benefit of the target tree for surface runoff reduction was estimated from the interception losses in the five rainfall events with surface runoff potential; the proportion was 6.2%. A detailed analysis of the rainfall-partitioning process of urban isolated tree provided data support and design strategy in urban stormwater management. • Rainfall-partitioning process of a tree was quantified using a weighing lysimeter. • Interception loss and interception rate were 11.2% and 12.0%, respectively. • The averaged proportion of surface runoff reduction for the target tree was 6.2%. • Obtained results are used to analyze surface runoff considering crown interception.