Comparison of passive fog gauges for determining fog duration and fog interception by a Puerto Rican elfin cloud forest

Abstract

Between 5 March and 10 May 2001, the performance of three types of passive fog gauges (wire harp WH, standard fog collector SC and Juvik gauge JU) was compared at a wind-exposed Puerto Rican elfin cloud forest site. The gauges were used to determine the timing and duration of fog, as well as fog-induced crown drip using gauge to canopy conversions factors. The latter were calculated as the average ratio between throughfall, and fog collected by the respective gauges during periods with fog-only and negligible evaporation loss. The fog gauges indicated very similar timing and fog duration, presumably because dense fog prevailed for 75–80% of the time whereas winds were generally sufficiently strong (4–5 m s⁻¹) and from a nearly constant direction. Resulting gauge to canopy factors were 0·12 for WH and SC, and 0·10 for JU. Estimating fog interception by the elfin forest canopy using these conversion factors gave very similar values for the three gauge types (mean rates of 0·15 ± 0·01 mm h⁻¹). Throughfall typically started about 5 h after the fog gauges indicated the beginning of a fog event. This time lag probably reflects the filling of the canopy storage capacity. Integrating the estimated fog interception rates over the time lag suggested an average value of 0·4 mm for the canopy storage capacity during fog-only events. The present results are expected to apply to sites with comparable wind and fog conditions. Copyright © 2010 John Wiley & Sons, Ltd.