Rain Gauge Analysis of Precipitation on Oahu

Precipitation on Hawai’i is regulated by the incoming trade-wind flow and the topography of the islands. Farmers and meteorologists both recognize the diversity of microclimates present on each island (mokupuni). The limited land area is culturally subdivided into moku, which comprise several watersheds (ahupuaa) for community and agriculture purposes. Ancient Hawaiian farmers orally passed down experience-based knowledge of microclimate patterns on the islands for centuries, but actual observational records are not always available. Since the beginning of the 20^th century, researchers have been collecting rain gauge data. Datasets are publicly available through USGS and NOAA websites. Using Matlab to analyze a few rain gauge datasets, we compare precipitation from rain gauges in different moku. We find a distinct contrast in precipitation, on the leeward and windward sides of the Ko’olau mountain range, which can be attributed to orographic processes. We expected to find similar precipitation patterns within moku, but through analysis in central Oahu we found that differences exist. Having access to actively updated precipitation records is a major foundation in outreach and educated decision making by the department of agriculture, city planners, researchers, and farmers alike.