Rainfall Interception Characteristics of Dracaena Sanderiana and Breynia Distincha

Interception of plants commonly used in urban landscape has not been widely studied compared to forested and cultivated area. Understanding the interception characteristics of these plants can facilitate the selection of the right plant type or combination in order to promote interception as a mean to improve the urban water cycle and urban built environment. Two (2) tropical plants are considered in this study, namely, Dracaena Sanderiana and Breynia Distincha, both with distinct plant structure, plant height, canopy size, number of leaves per plant, leaf size and leaf shape. Rainfall interception characteristics are investigated in laboratory environment using standard hydrology apparatus for different plant density. Artificial rainfall intensity of fixed duration is varied to measure the volume and duration of outflow, and volume intercepted. Results show that runoff begins earlier for higher rainfall intensity and lower plant density. The volume and duration of outflow increases with rainfall intensity and interception increases with canopy cover ratio and leaf area ratio for both plants. At lower plant density, Breynia Distincha has lower interception compared to Dracaena Sanderiana. However, at high plant density, Breynia Distincha demonstrates much better interception capacity even though the canopy cover and leaf area ratios are smaller than Dracaena Sanderiana. The phenomenon may be attributed to coalescence of water droplets that either flow down as stemflow or drip off the leaves under gravitational action. The firm small leaves of Breynia Distincha oriented at near horizontal are more likely to retain the intercepted rainwater compared to the slender soft leaves of Dracaena Sanderiana. This shows that closely spaced Breynia Distincha can be effective in increasing urban interception.