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Recent study confirms age-old idea that volcanic smog influences rainfall on Hawaiʻi Island

USGS-Hawaiian Volcano Observatory

There is little modern research on the relationship between volcanic smog and rainfall, but for generations, Big Island locals have noticed there less rainfall when there is heavy vog.

Vog is mostly composed of sulfur dioxide, or SO2.

A study this year compared rainfall and sulfur dioxide emissions from Kīlauea from 1979 to 2017. Research shows what has been observed anecdotally for years — days with heavy vog have less rainfall around Kīlauea.

"On average, if you take the high emission days versus the low emission days, you get about a 8 mm per day difference — which on one day is not a lot, but if you accumulate over the course of a year, and you have a very active volcano, it adds up day after day after day," said Alison Nugent, one of the authors of the research paper.

"It’s not like if there’s vog it’s not gonna rain. It’s more like if there’s vog, there may be a little less rain than there otherwise would be," Nugent told HPR.

North-easterly trade winds help blow vog away from neighboring islands. Some research suggests climate change is disrupting the frequency and strength of trade winds.

Tamar Elias, a chemist with the U.S. Geological Survey Hawaiian Volcano Observatory, said, "When we have interruptions in trade winds, that’s when we see vog on the east side of Hawaiʻi Island, and we see vog on the neighbor islands. As long as there’s trade wind flow, generally neighbor islands don’t receive vog."

Scientists are finding more correlations between vog and climate.

The small difference in rainfall caused by the vog can affect farmers on the Big Island — and if trade winds stall, those impacts could stretch to other islands.

Those living near an active volcano can track vog emissions here.

For more information on vog, visit the Hawaiʻi Interagency Vog Information Dashboard.

Zoe Dym was a news producer at Hawaiʻi Public Radio.
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