Published online by Cambridge University Press: 03 May 2011
Between 5 March and 10 May 2001, the performance of three types of passive fog gages (wire harp WH, standard fog collector SC, and Juvik gage JU) was compared at a wind-exposed Puerto Rican elfin cloud forest site. The gages were used to determine the timing and duration of fog and of fog-induced crown drip. Gage to canopy conversion factors were derived from the ratio between throughfall, and fog collected by the respective gages during periods with fog-only and negligible evaporation loss. The fog gages indicated very similar timing and fog duration, presumably because dense fog prevailed for 75–80% of the time and winds were generally sufficiently strong (4–5 m s−1). Resulting gage-to-canopy factors were 0.12 for WH and SC, and 0.10 for JU. Estimating fog interception by the canopy using these conversion factors gave very similar values for the three gage types (mean rates of 0.15 ± 0.01 mm hour−1). Throughfall typically started about 5 hours after the fog gages indicated the beginning of a fog event. This time lag probably reflects the filling of the storage capacity of the canopy, because wet canopy evaporation was negligible. Integrating the estimated fog interception rates over the time lag suggested an average value of 0.4 mm for the canopy storage capacity during events with fog-only.