Abstract

Recent surveys of tropical forest water use suggest that rainfall interception by the canopy is largest in wet maritime
locations. To investigate the underlying processes at one such location—the Luquillo Experimental Forest in eastern Puerto
Rico—66 days of detailed throughfall and above-canopy climatic data were collected in 1996 and analysed using the Rutter and
Gash models of rainfall interception. Throughfall occurred on 80% of the days distributed over 80 rainfall events. Measured
interception loss was 50% of gross precipitation. When Penman–Monteith based estimates for the wet canopy evaporation rate
(0.11 mm h21 on average) and a canopy storage of 1.15 mm were used, both models severely underestimated measured
interception loss. A detailed analysis of four storms using the Rutter model showed that optimizing the model for the wet
canopy evaporation component yielded much better results than increasing the canopy storage capacity. However, the Rutter
model failed to properly estimate throughfall amounts during an exceptionally large event. The analytical model, on the other
hand, was capable of representing interception during the extreme event, but once again optimizing wet canopy evaporation
rates produced a much better fit than optimizing the canopy storage capacity. As such, the present results support the idea that it
is primarily a high rate of evaporation from a wet canopy that is responsible for the observed high interception losses.

Citation

Schellekens, J., Scatena, F.N., Bruijinzeel L.A. (1999): Modeling rainfall interception by a lowland tropical rain forest in northeastern Puerto Rico. Journal of Hydrology.