Extreme Hourly Rainfall Trends across five Hawaiian Islands

Extreme precipitation and associated floods can have devastating consequences on societies and ecosystems. However, our understanding of extreme rainfall changes spatially and temporally over time, particularly in Hawaiʻi, remains limited. To address this, we examined changes in extreme rainfall across the five Hawaiian islands using hourly rainfall data with stationary and non-stationary Generalized Extreme Value (GEV) distributions. We also examined the temporal patterns of annual maximum hourly rainfall using circular statistics.

Our results indicate that the windward regions of Oʻahu, Kauaʻi, and Hawaiʻi Island experienced the most intense rainfall over the past 30 years. Decreasing trends were identified across Oʻahu, Molokaʻi, and Maui, while increasing trends were observed on Hawaiʻi Island and Kauaʻi. Furthermore, extreme (maximum) 1-, 3-, and 6-hour rainfall mainly occurred between August and April of the next year. In addition, the median timing of extreme rainfall are slightly varied with different locations, including different islands, windward and leeward sides.

This new knowledge on extreme rainfall patterns, timing, and locations can be used to enhance our infrastructure planning and emergency responses in Hawaiʻi, minimizing the threats from such extreme events.