May 23, 2017 / 12:58 AM / 7 months ago

Hawaii faces more flooding with possible record high tides

SEATTLE (Reuters) - Hawaii will likely suffer more coastal flooding this week driven by record high tides, a symptom of global warming that could become routine within decades, scientists said Monday.

After a high tide in April broke a 112-year record, combining with wave action to flood low-lying coastal areas, similar tides are predicted later this week and twice more during the summer, with water likely to cover roadways and reach buildings near shore.

Water levels at or above April’s record tide are now predicted for May 25-27, as well as June 23-24 and July 21-22, Mark Merrifield, a University of Hawaii oceanographer, said in a Monday phone interview.

While so far mostly a nuisance, rising global sea levels will likely drive similar flooding dozens of times per year by 2050, and could pose serious risks during storm seasons, said Chip Fletcher, a dean at the University of Hawaii’s School of Ocean and Earth Science and Technology.

“First you’ll see it during the highest tides of the year, then during the new moon and full moons,” when peak monthly tides typically occur, Fletcher said. “And then it will start to occur at every high tide, every day.”

As much as 45 percent of the floodwater height during the April event was attributable to sea level rise driven by global warming, depending on the yearly baseline used, Merrifield said.

Merrifield said his modeling predicts similar water levels occurring four times per year by 2030, 25 times yearly by 2050, and potentially 100 times or more yearly by 2070.

An overwhelming majority of scientists say human activity - including the burning of oil, gas and coal - is the main driver of rising global temperatures.

While the immediate risk from such flooding is low, both Merrifield and Fletcher said the long-term risks are substantial.

As record-high water levels occur more frequently, the odds of one coinciding with a tropical storm or hurricane also increase, especially since the area tends to experience higher tides during hurricane season.

“The worst-case scenario is a tropical storm making landfall during the highest tides of the year in the Summer,” Fletcher said. “What might have been minor damage from a storm, 20 or 30 years from now could cause extreme damage.”

The forecast comes amid growing concern for coastal regions worldwide, including in the United States, where rising seas have driven increased flooding in coastal cities like Norfolk, Virginia and Annapolis, Maryland.

Reporting by Tom James; Editing by Andrew Hay

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