Hawaii could be in for a climate future with less rainfall and drier conditions as temperatures continue to increase globally, according to a University of Hawaii climate and hydrology expert.
That forecast likely doesn't surprise anyone following climate change and global warming, but it highlights the challenges facing local water resource management efforts.
A drier climate would jeopardize Maui's water supply and native ecosystems, said UH-Manoa geography professor Tom Giambelluca.
Water flows out of Wailoa Ditch on Tuesday afternoon as it it enters Kamole Weir, the intake for the Kamole Water Treatment Facility. The ditch gathers water from streams in the East Maui watershed and channels the water to the treatment facility that feeds water to the Upcountry area. A University of Hawaii climate hydrology expert said that three historical trends could signal a drier climate for Hawaii: rising temperatures, a decrease in rainfall and a decline in stream flows. A drier climate could jeopardize Maui’s water supply and ecosystem.
The Maui News / MATTHEW THAYER photo
He's been studying Hawaii's weather patterns for more than two decades, including tracking rainfall at hundreds of stations statewide. He is best known for his collaboration on the "Rainfall Atlas of Hawaii."
Giambelluca pointed to three historical trends that could signal a drier climate ahead for Hawaii: rising temperatures, a decrease in average rainfall and a decline in stream flows.
Giambelluca says Hawaii's temperatures have been warming at about the same rate as the rest of the globe for the last 30 years, which he attributes to human-induced global warming.
"We can't say with a 100 percent certainty that it's going to be drier, or how much drier it's going to get," Giambelluca said. "But I would say the lead of evidence points to a drier future, and that's something that anybody concerned with water supply, agriculture or our important Hawaiian native ecosystems would be concerned about."
The Sustainable Living Institute of Maui, Maui Tomorrow Foundation and the county's Department of Water Supply sponsored a presentation by Giambelluca on Monday night on the University of Hawaii Maui College campus.
Giambelluca shared some of his latest research at the educational event that focused on how changing weather patterns could affect Maui's water future.
He said Hawaii's temperatures are accelerating at a faster rate at higher elevations, including atop the wet West Maui Mountains.
"Why should we care about that?" he asked. "These are places where our intact native ecosystems exist. These are places that are important for our water supply. Rapid climate change in those areas is alarming."
Giambelluca also has been tracking precipitation trends in the islands.
He said Maui has seen the largest decline in precipitation among the islands over the last 30 years.
Maui's rainfall levels decreased by 9 percent per decade between 1978 and 2007. That compares to a statewide decrease of 6 percent per decade for the same time period.
But, Giambelluca cautioned that the rainfall data includes natural ups and downs.
"Some of that recent change is probably explained by natural fluctuations, and so it's not necessarily interpreted as an ever-increasing trend toward drier and drier climate," he said. "I do think the climate is getting drier in Hawaii, but I don't necessarily think the recent 30 years is going to be a continuing trend in the future."
He also talked about the possibility of a future climate where average rainfall decreases, but isolated heavy rainfall events increase, meaning the islands would see rain less frequently.
While Giambelluca didn't come off as a Chicken Little, he did caution that he believes Hawaii stands to lose unique resources as the Earth continues to warm.
"Humans can adapt to change, but it will come at a great cost," he said. "For Hawaii, we stand to lose native species, native ecosystems. Many things are on the chopping block."
Dave Taylor, director of the county's Department of Water Supply, said the idea of a drier climate in the future doesn't come as news to him.
He also said researchers haven't been able to pinpoint how specific areas will be impacted.
"We're not really aware that you can take his regional analysis and actually apply it to a specific localized aquifer," Taylor said after Giambelluca's presentation.
Instead, he said the department does long-term planning to prepare for future supply and demand.
"Whether we need it in two years, or we end up sitting on it for five years, as long as you know what's next, you don't have to guess exactly what the future is," he said. "The science to accurately predict exactly what the rainfall will be in a given area - that is not going to happen. You have to use general trends to make decisions about what to do without having detailed knowledge about any one specific area or project."
* Nanea Kalani can be reached at email@example.com.