Spatial Rainfall Patterns of ENSO and PDO in Hawai'i

Rainfall in Hawai'i is sensitive to large-scale modes of climate variability, particularly the El-Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Until now, understanding of the influences of ENSO and PDO on rainfall in Hawai'i has been limited to individual station evaluations and has not been examined as a continuous pattern at a high resolution statewide. With the release of new month-year rainfall maps produced for each Hawaiian Island from 1920-2007, spatial analyses of the signature of ENSO and PDO phases in rainfall can be conducted. Using the Multivariate ENSO Index (MEI) values and PDO Index values, different phases of ENSO and PDO were identified. For each island, the relative anomaly maps (month-year maps divided by the monthly mean maps) were composited by month and season for each phase of ENSO and PDO. These monthly and seasonal composite maps show the average relative anomaly patterns and magnitudes of rainfall during each phase. Detailed information about the likely effects of ENSO and PDO teleconnections on rainfall is extremely important to water resource managers in Hawai'i, as extreme dry periods in high groundwater recharge areas can severely affect the water supply. These maps will provide the tools necessary to help Hawai'i plan for future rainfall variations.