Thursday, November 10, 2016

Hawaiian climate: it's not changing the way you expect--it's getting scarier

Much of what you’ve heard about the Hawai`i impacts of climate change may be false. It could be worse than what you’ve heard. 

Example: It’s probably not going to be drier everywhere, as many have suggested in recent years. In fact, according to a new paper, it’s more likely to get more extreme everywhere—kind of like American politics. 

Although “Hawaii is renowned for its generally pleasant weather, anticipated climate change over the present century will likely present significant challenges for its inhabitants,” says the paper, published by the American Meteorological Society.

Kevin Hamilton, of the University of Hawai`i’s International Pacific Research Center, said the best research indicates it’s likely to get wetter in wet areas, but drier in dry areas—deepening the divisions between the different zones of the Islands. IPRC is part of the university's School of Ocean and Earth Science and Technology.

“We expect generally more rainfall on the windward sides and less on the leeward sides.  Combined with increased evaporation from the warmer surface this could lead to particularly dry conditions in places that are already feeling water stress, such as west central Maui,” said Hamilton, the retired director of the IPRC, in an email. 

Hamilton and co-authors Chunxi Zhang, Yuqing Wang and Axel Lauer just published their latest data in the Journal of Climate. It is entitled, Dynamical Downscaling of the Climate for the Hawaiian Islands. Part II: Projection for the Late Twenty-First Century

Their work also anticipates warmer weather in the Hawaiian uplands. 

“The surface air will warm significantly and the warming will be substantially more pronounced at high topographic elevations,” Hamilton said in an email. 

That has significant impacts, for example, for Hawaiian upland forest habitats. Previous research suggests that warming high mountains will increase upland mosquito populations, with direct impacts on native birds. Mosquitoes carry avian disease like avian malaria and pox.

“While published research on climate-related stress has concentrated on a limited number of species, it is likely that climate change in Hawaii will threaten many species and perturb terrestrial and coastal ecosystems, with unfortunate effects on the state’s remarkable contribution to global biodiversity,” the authors wrote.

Another issue: If drier areas get drier, they’ll be in greater need of irrigation to support agriculture, landscaping and other uses. That water will need to be diverted from the wetter areas. Water issues are intensely political matters in the Islands, and this suggests they’ll continue to be problematic for policy-makers.  

“Available surface and groundwater resources are scarce enough that water use restrictions are common in some areas during droughts, while agricultural demands for groundwater have sparked a history of public controversy and litigation,” the authors wrote.

Extreme weather events are likely to increase, Hamilton and his team wrote, like the big Manoa, O`ahu, flood of 2004, and this year’s Iao Valley flood, both of which caused massive damage costing into the tens of millions of dollars.

The IPRC group is continuing to fine-tune its data, but Hamilton said its climate models, when compared with past weather conditions, are accurately representing what’s been happening. And one of the warnings from the models are that apparent trends may not reflect what will happen in the future.

For example, while the models predict the drying trend in Hilo that has been seen in recent years, that may not continue. The models predict Hilo will get significantly wetter later in this century.

If you’re interested in detailed analyses, here are links to the group’s previous paper and the current paper.

© Jan TenBruggencate

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