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Abstract for 2003 International Union of Geodesy and Geophysics meeting, Sapporo, Japan



Gingerich, Stephen B. and Scholl, Martha A.

The contribution of cloud water to recharge is being investigated on the windward side of Haleakala Volcano, Maui, Hawaii. The study involves using the different isotopic signatures of cloud water (windblown precipitation including fog) and rain to trace cloud water through the forest water cycle, as well as comparing relative amounts of fog, rain, and canopy throughfall. At the research site, the volume of rain, cloud water, and canopy throughfall is recorded hourly. Stable isotope samples of rain, cloud water, soil water, stream water, and tree sap are collected monthly. The site also has a visibility sensor and weather station. At 1,950-m altitude, the windward slopes of the volcano are enveloped by orographic clouds almost every day. The site is near the upper boundary of extensive forests that are a major watershed for the island. Volume data indicate that windblown precipitation (compared to vertically falling rain as measured by a standard gage) contributes substantially to the forest water. A screen-type precipitation collector with a collection area of 0.60 square meter mounted perpendicularly to the prevailing wind direction has collected to date between 126 and 367 percent of what was collected by a standard rain gage (normalized to collection area). This water is defined as cloud water for purposes of the study, and the additional volume not collected in the rain gage averages 1.0 L per square meter of surface area per day at the site. Soil water deuterium composition was consistently isotopically lighter than cloud water composition for samples analyzed thus far, indicating that the soil water is derived predominantly from large rain storms. Stream water composition suggests a perennial source of recharge, from cloud water and storm rainfall, to a shallow groundwater flow system. The information gained from this study underscores the importance of the cloud water contribution to soil moisture, groundwater recharge, and stream flow in watersheds on high tropical volcanoes.


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