This study investigates the anatomy of precipitation events in a Hawaiian montane cloud forest with the particular focus on the relative contribution of cloud water interception (CWI) and rainfall. Research was conducted at Alakahi in the Kohala Forest Reserve on the Island of Hawai'i. The region is characterized as a dwarf (elfin) montane cloud forest with abundant epiphytes. This research aimed to clarify the disparity in fog, rain and canopy throughfall values reported in previous studies at this site.

Precipitation events were dissected in a multitude of ways to comprehend the various dynamics that occur in this TMCF. The majority of precipitation events occurred < 5mm. However, most of the precipitation during this study occurred in a few large-scale events (>25mm). Although these few large scale events provided most of the precipitation, the overwhelming amount of small scale events allowed for consistent canopy wetting to reduce potential evapotranspiration from the forest.

At Alakahi, throughfall was not significantly enhanced by supplemental fog drip. In general this study confirms earlier results of Delay (2005), and both studies stand in stark contrast to the earlier “forest edge” fog drip study conducted at a near-by site with direct exposure to prevailing tradewinds coming off Alakahi gulch (Juvik and Nullet 1995, Juvik et al. 2008). At that site canopy throughfall was found to range from 120–180% of open-site rainfall and fog gauge event totals explained more of the variation in canopy throughfall than rain. In contrast this study under continuous canopy with significant (1–2 km) upwind fetch (i.e. not at forest edge) across a closed canopy; throughfall was best explained by above canopy rain (83%) rather than fog gauge interception.