Rainfall interception by six urban trees in San Juan, Puerto Rico

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 72.4mm, and storm duration spanned 1h to several days. Six of the storms analyzed were characterized by maximum hourly intensity rainfall rates categorized as heavy (> 7.6mm/h). Strong northeasterly winds brought rain in sustained gusts up to 35km/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.