This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While long-term data show that Hawaiʻi is getting drier overall, short, intense downpours that cause sudden, dangerous flash floods are getting stronger on the islands, according to a new study by researchers at the University of Hawaiʻi at Mānoa. Published in the International Journal of Climatology, the research from the College of Tropical Agriculture and Human Resilience (CTAHR) is the first comprehensive study to analyze extreme hourly rainfall patterns across the state over 50 years (1966–2020).
The team examined decades of hourly data from 117 rain gauges across Kauaʻi, Oʻahu, Molokaʻi, Maui and Hawaiʻi Island, uncovering climate trends that traditional 24-hour daily averages often miss. In steep, mountain-filled tropical watersheds like Hawaiʻi's, bursts of intense rain lasting one to six hours can overwhelm stream channels and storm drains before emergency alerts are issued. "If we want to understand extreme weather, like storms and floods, we really need to look at short-duration, high-temporal-resolution data rather than daily or monthly averages," said Yinphan Tsang, a professor in CTAHR's Department of Natural Resources and Environmental Management and the principal investigator.
Researchers noted that rainfall trends vary widely, even between neighboring areas. Because of Hawaiʻi's unique mountains and island terrain, rainfall intensity can increase in one neighborhood while decreasing just a few miles away. Researchers also identified two distinct periods when Hawaiʻi is most vulnerable to extreme hourly rain events: October through December and February through March.
These heavy rains are generally driven by cold fronts, Kona storms and other winter weather systems moving through the islands. The extreme events occurring from February through March, near the end of the wet season, were unexpected and could take people by surprise. Other systems, such as tropical storms, could also bring extreme rainfall during the summer season.
The findings offer updates for emergency responders, county planners and infrastructure designers. The study was a collaborative effort at UH Mānoa, bringing together experts from CTAHR, the School of Ocean and Earth Science and Technology, the College of Social Sciences and the Water Resources Research Center. The research was compiled primarily by Maxime Gayte, with co-authors including faculty members Tsang, Pao-Shin Chu (Hawaiʻi State Climatologist), Thomas W.
Giambelluca Jr., researcher Yu-Fen Huang and researcher Hanpei Zhang. Maxime Gayte et al, Spatial and Temporal Patterns of Extreme Hourly Rainfall in the Hawaiian Islands, International Journal of Climatology (2026). DOI: 10.1002/joc.70501 Provided by University of Hawaii at Manoa Bachelor's in mathematical biology, Master's in creative writing.
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