Researchers from the University of Hawaii at Manoa and the University of Colorado at Boulder conducted the research, made complicated by diverse rainfall patterns in Hawaii where dry and wet areas are often less than a mile apart.
They devised a method called "statistical downscaling" that reanalyzed observations from 1978 to 2010 at 12 rain-gauge stations across the islands to reveal effects of the general drying trend on local heavy-rain days.
Developing a statistical model that estimates the number of heavy rain events during a year, they said large circulation patterns over the mid-latitude and tropical North Pacific have shifted since 1978 so that fewer weather disturbances reach the Islands during the rainy season from November through April.
"We can't predict individual rain events with our method," Thomas W. Giambelluca of the UHM department of geography said, "but it gives us a very good estimate of the number of heavy rain events in a given season based on the large-scale atmospheric circulation patterns."
Their statistical model and cutting-edge climate models, combined with the projected increase in greenhouse gases until the end of this century, suggests the recent trend toward drier winter seasons in Hawaii with fewer heavy-rain days will be the norm through the end of this century, the researchers said.