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Abstract The Hawaiian Islands have some of the most spatially diverse rainfall patterns on Earth, affected by prevailing trade winds, midlatitude disturbances, tropical cyclones, and complex island topography. However, it is the only state in the United States that does not have assigned climate divisions (boundaries defining climatically homogeneous areas), which excludes it from many national climate analyses. This study establishes, for the first time, official climate divisions for the state of Hawai‘i using cluster analysis applied to monthly gridded rainfall data from 1990 to 2019. Twelve climate divisions have been identified: two divisions were found each for the islands of Kaua‘i (Leeward Kaua‘i and Windward Kaua‘i), O‘ahu (Waianae and Ko‘olau), and Maui County (Leeward Maui Nui and Windward Maui Nui), and six divisions were identified for Hawai‘i Island (Leeward Kohala, Windward Kohala, Kona, Hawai‘i Mauka, Ka‘u, and Hilo). The climate divisions were validated using a statewide area-weighted division-average rainfall index which successfully captured the annual cycle and interannual rainfall variations in the statewide average rainfall series. Distinct rainfall seasonality features and interannual/decadal variability are found among the different divisions; Leeward Maui Nui, Leeward Kaua‘i, Kona, and Hawai‘i Mauka displayed the most significant rainfall seasonality. The western Hawai‘i Island divisions show the most significant long-term decreasing trends in annual rainfall during the past 100 years (ranging from −2.5% to −5.0% per decade). With these climate divisions now available, Hawai‘i will have access to numerous operational climate analyses that will greatly improve climatic research, monitoring, education, and outreach, as well as forecasting applications. Significance StatementThe Hawaiian Islands have some of the most spatially diverse climate patterns on Earth, but it is the only state in the United States that does not have assigned climate divisions, which excludes it from many national climate analyses. This paper establishes official climate divisions for the state of Hawai‘i, filling an incredibly important gap in the National Oceanic and Atmospheric Administration (NOAA)’s national coverage, moving toward better data equity and coverage outside the contiguous United States. Distinct rainfall seasonality features and interannual/decadal variability are revealed and compared among the different divisions. With these climate divisions now available, Hawai‘i will have access to numerous operational climate analyses that will greatly improve climatic research, monitoring, education, and outreach, as well as forecasting applications.
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This content will become publicly available on April 18, 2026
Stalagmites as Records of Tropical Climate Change
Stalagmites are excellent archives of past climate change. They can grow continuously for tens of thousands of years, be precisely dated, and record a wide range of climate variables through their chemistry. In the last quarter century, numerous studies have focused on (sub)tropical hydroclimate variability, particularly from South Asia, the Maritime Continent, and northern Australia. This talk will discuss how stalagmite paleoclimate research is conducted and what important findings have resulted from this work.
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- Award ID(s):
- 2147186
- PAR ID:
- 10614577
- Publisher / Repository:
- Circolo Speleologico Romano
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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