Developing high-resolution rainfall change scenarios for the Hawaiian Islands using statistical downscaling

An overlook of a lush vegetation shows rainclouds in the background.
Rainclouds over Maui highlight the importance of rainfall in maintaining the ecosystem health of the islands. (Photo: Sebastien Panouille CC BY NC 2.0)

Surrounded by saltwater, human and natural communities on the Hawaiian Islands depend upon the freshwater supplied by rainfall for survival. Climate change will likely alter rainfall timing and intensity, but global climate models cannot capture the fine-scale dynamics of local rainfall, making future rainfall predictions for the islands uncertain. For this project, scientists used a technique called statistical downscaling (combining coarse-scale climate models with local historical data) to generate high-resolution maps showing seasonal rainfall change projections for Hawaiʻi over the course of this century. Results suggest that Hawaiʻi’s climate will become drier overall in the second half of the century, but this effect will vary considerably across the islands and by season. There may be an increasing contrast between wet and dry regions on each island, as wet areas become wetter and dry areas become drier. The maps and findings produced by this project offer critical information for resource managers as they undertake adaptation and water management planning. They also provide a foundation for further ecological research, such as exploring the impacts of climate change on native Hawaiian plants and animals.

Color-coded map of Hawaiian islands show windward sides will have little or positive changes in precipitation while leeward sides will have mild to severe decreases.
Projected precipitation changes will vary greatly by location. Numbers represent percent change relative to present-day values.




Oliver Elison Timm
Research Assoc. Professor of Atmospheric and Environmental Science, SUNY Albany


Thomas Giambelluca
Professor of Geography, UH Mānoa
Henry Diaz
Meteorlogist, Cooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder