Modelling rainfall interception by a lowland tropical rain forest in northeastern Puerto Rico

Recent surveys of tropical forest water use suggest that rainfall intercept ion 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 cli matic data were collected in 1996 and analysed using the Rutter and Gash mo dels of rainfall interception. Throughfall occurred on 80% of the days dist ributed over 80 rainfall events. Measured interception loss was 50% of gros s precipitarion. When Penman-Monteith based estimates for the wet canopy ev aporation rate (0.11 mm h(-1) on average) and a canopy storage of 1.15 mm w ere used, both models severely underestimated measured interception loss. A detailed analysis of four storms using the Rutter model showed that optimi zing the model for the wet canopy evaporation component yielded much better results than increasing the canopy storage capacity. However, the Rutter m odel failed to properly estimate throughfall amounts during an exceptionall y large event. The analytical model, on the other hand, was capable of repr esenting interception during the extreme event, but once again optimizing w et 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 respo nsible for the observed high interception losses. (C) 1999 Elsevier Science B.V. All rights reserved.