Abstract
Rainfall interception is an important part of the urban hydrological cycle. Understanding is limited about the role of urban trees and other vegetation in the interception process. This study quantified interception losses by six trees in the Caribbean coastal city of San Juan, Puerto Rico, three representing a broadleaf evergreen, and three representing a broadleaf deciduous species. Rainfall was partitioned into throughfall for 13 storms to compare the results between tree types. Total rainfall ranged from 2.9 to 72.4 mm, and storm duration spanned 1 h to several days. Six of the storms analyzed were characterized by maximum hourly intensity rainfall rates categorized as heavy (> 7.6 mm/h). Strong northeasterly winds brought rain in sustained gusts up to 35 km/h. Average interception losses totaled 19.7% for both tree types, 22.7% for the deciduous trees, and 16.7% for the evergreen trees. Throughfall exceeded 90% of total rainfall for each of the six trees on one or more occasions, and heavy intensity storms produced negative interception losses in one individual. The effect of tree type on interception was significant for storms of low and moderate intensity, but not heavy intensity. Differences in interception losses between storms of similar intensity and between the two tree types were influenced by leaf area and wind. Results suggest that individual urban tree canopies function as spatio-temporally dynamic storage reservoirs whose interception capacity can vary as micro-meteorological conditions change. These findings help advance understanding about interception processes in humid tropical urban settings.
Highlights
Rainfall interception by trees is an important part of the urban hydrological cycle, and the spatial and temporal distribution of the hydrographic curve in cities (Xiao and McPherson 2002; Livesley et al 2016)
Calophyllum had an average diameter at breast height (DBH) of 28.2 ± 1.5 m, average tree height of 9.7 ± 0.3 m, average height to crown base distance of 3.1 ± 0.2 m, average crown diameter of 10.2 ± 0.3 m, and estimated leaf area of 41.5 m2 ± 7.9 m
The resulting leaf areas calculated for both tree types fell within the 95% confidence intervals of predicted leaf area reported by Peper et al (2001b) for the reference species utilized
Summary
Rainfall interception by trees is an important part of the urban hydrological cycle, and the spatial and temporal distribution of the hydrographic curve in cities (Xiao and McPherson 2002; Livesley et al 2016). Located in arid to tropical climates, with reported annual interception losses ranging from 10 to 50% of total precipitation (Carlyle-Moses and Gash 2011). Urban forest canopies have been reported to intercept storm precipitation (Inkiläinen et al 2013; Livesley et al 2014; Xiao and McPherson 2016), with consequent reductions in runoff volumes across the landscape (Wang et al 2008; Berland and Hopton 2014; Schooling and Carlyle-Moses 2015). Together with other green spaces, urban and peri-urban trees can contribute to avoided flood control costs and lowered flood risk (Zhang et al 2015; Kim et al 2016; Livesley et al 2016)
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