Small urban tree rainfall interception measurements for inclusion into WinSLAMM, the source loading and management model

R. Pitt, R. Bean, J. Vooheesw, M. Elliot


This paper is a continuation of the urban tree interception studies initially reported in this journal by Bean, et al. (2020). In the previous paper, tree interception measurements were made under large, mature, urban trees (deciduous Water oak (Quercus nigra) and evergreen Loblollly pine (Pinus taeda) trees). 85 rain events were monitored from early December 2018 through January 2020. It was found that tree type had the most important effect on tree canopy interception, followed by rain amount, while seasonal effects were not as important. The interception under the pine was only important for the smallest rains, while interception under the oak varied from about 30 to 50%, depending on the rain amount.

This most recent series of measurements examined the interception from two specimens of smaller urban trees, Japanese maples (Acer palmatum). 84 rain events from the end of March through the end of December 2020 were monitored with a standard rain gage located in a grass area for rainfall measurements, and similar rain gages located under the two trees to directly measure throughfall. All seasonal and overall period regression relationships comparing the throughfall to the rain were highly significant. ANOVA analyses of the regression analyses did not indicate significant equation intercept values, with the regression equations only containing slope terms. This indicated that the rainfall fraction intercepted by the trees did not significantly vary by rain depth. Statistical analyses also found that the rainfall fraction intercepted did not significantly vary by season. Overall, the interception under the Japanese maples was about 15% for all rains and for all seasons.

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