36 - Interpreting canopy water balance and fog screen observations: separating cloud water from wind-blown rainfall at two contrasting forest sites in Hawai'i

Summary

ABSTRACT

Based on field measurements made at dry (Auwahi) and wet (Waikamoi) cloud forest sites on the island of Maui, a preliminary analysis of fog gage measurements and wet-canopy water balance estimates was made. Accounting for effects of wind-blown rainfall and varying wind direction, estimates of cloud water flux were derived based on fog gage observations. Throughfall (TF) measurements, incident rainfall estimates, and calculated amounts of wet-canopy evaporation were used to estimate event totals of cloud water interception (CWI) by the vegetation at each site. Measured TF was about 37% of incident rainfall at Auwahi, and 119% at Waikamoi. At both sites TF was dominated by rainfall, but was significantly influenced by fog at Waikamoi only. Fog contributed at an average frequency of once every two days at Auwahi and about twice in three days at Waikamoi. Derived CWI totals were equivalent to 151 mm year^–1 at Auwahi and 1073 mm year^–1 at Waikamoi. At Auwahi, however, the majority of intercepted water was re-evaporated from the wet vegetation, and never reached the ground. Total CWI was related to fog screen catch and cloud water flux at Waikamoi, but not at Auwahi.