By Jan TenBruggencate
Advertiser Columnist

Scientists who met at the University of Hawai'i in a climate conference last week say global climate patterns seem to indicate that Hawai'i can count on drier weather over the next century than the last, but when it rains, it could rain harder.

"I think managing water resources is going to be a very big topic" for the future, said Henry Diaz, a research scientist with the National Oceanic and Atmospheric Administration's Climate Diagnostics Center.

Diaz was co-organizer of "The Hadley Circulation: Present, Past and Future," a conference that brought nearly 50 scientists from 13 countries to work on linking modern climate observations and models with discoveries about ancient climate that are developed from the study of ice cores, tree rings and corals. The International Pacific Research Center at the University of Hawai'i hosted the conference.

One thing they're learning is that things like global warming clearly change weather patterns, and can do so quickly, but not always predictably, said Kevin Trenberth, an atmospheric scientist and head of the Climate Analysis Center of the national Center for Atmospheric Research.

Diaz said his own research has already seen changes in the Hadley circulation system during the past 20 or 30 years. The Hadley system is the planet's way of moving warm air from the equator up to mid-latitudes. Essentially, warm air over the equatorial region rises, travels northward at high elevation, and then sinks again between 20 and 30 degrees north latitude as it cools. In the Pacific, that air then travels along the Earth's surface toward the equator in the form of the southeast tradewinds.

If that airflow increases, as it has with the increased frequency of El Ni–o events since the mid-1970s, Hawai'i gets drier weather, Diaz said. And it looks like that dry-weather trend could continue through the coming century, both men said. But there could also be greater variability in weather, and "when you do get rain, it's probably going to be a doozy," Trenberth said.

Ultimately, though, if the climate continues to warm, the ice cap in the northern polar regions will melt, and the difference in temperatures between equatorial and polar regions will decline. That could reduce Hadley circulation — perhaps reversing the extended dry spell.

Predicting just when, how and what will happen is troublesome, the scientists said.

"We're studying the best we can the beast we call the Earth's climate system. The prospect will be that the Earth's climate will change, but not in a way we can predict right now," Trenberth said.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. You can call him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.