Today’s storm surge is tomorrow’s high tide, says new report

As sea levels rise due to global warming, the type of flooding currently only seen in storms will occur during normal high tides. This is called “sunny day flooding”.

“Sunny weather flooding, or high tide flooding, is flooding that is increasingly occurring with no storm or rain in sight,” report author and NOAA oceanographer William Sweet told CNN.

This increase was measured by NOAA’s array of tide gauges that line all coasts of the continental United States and territories, including Alaska, Hawaii, and the Pacific and Caribbean islands.

Examples of these stormless floods happening now include the “King-tide” floods in Miami and Charleston, which clog stormwater systems and inundate some low-lying roads and vulnerable infrastructure.
The City of Miami Beach is in the midst of a five-year, $400 million stormwater pumping program and other projects that city officials hope will keep ocean waters from flooding the city.

“With flooding on sunny days, we see a high tide on steroids,” according to Erika Spanger-Siegfried, senior climate analyst at the Union of Concerned Scientists. The group was not affiliated with the study.

“It can reach our communities and leave us stranded in our cars, stuck at home, wading through water, unable to go to school and work… not a catastrophic flood but it can disrupt our ability to carry out our normal life,” says Spanger-Siefried.

But according to Sweet and his colleagues, these untimely floods are becoming a much bigger and more frequent concern.

On the majority of tide gauges analyzed on the East Coast, sea level rise was found to be accelerating – and this trend is expected to continue.

By 2050, flooding at high tide would occur on up to 130 days per year in cities along the northeast Atlantic coast, under the “intermediate” scenario (considered a likely scenario based on the current and projected greenhouse gas emissions) presented in the report. In the western Gulf of Mexico it would be 185 days per year and 80 days per year for the eastern Gulf. These places currently experience three to six days of flooding in an average year.

The west coast, while continuing to see sea level rises, is less vulnerable to flooding at high tide. This is because rates of sea level rise have generally been lower, and the higher elevations and coastal geography make it less vulnerable.

Pacific Coast locations would experience approximately 30-35 days per year of high tide flooding by 2050 (compared to one to two days currently). El Niño years would likely see additional flooding on the west coast due to warmer waters and more storms.

But by 2100, high tide flooding will become daily flooding – almost all regions experiencing high tide flooding 365 days a year.

Current storms provide a glimpse of the future

Recent northeasts, like the one currently pounding the region, show us the sea level rise trajectory we’re on, according to Spanger-Siefried.

Current tide heights have reached and even surpassed the famous blizzard of 1978, which saw tides rise more than 4 feet above normal, even though these were smaller storms, as they had l advantage of a higher base sea level.

As sea levels continue to rise, storm tides will rise even higher, leading to destructive flooding even during not-so-extreme storms.

“With higher sea levels, the likelihood of such events causing minor to major changes [1.5 to 4 feet above current high tide levels] flooding is increasing,” Sweet said.

Trends showing acceleration in sea level rise seen in cities on the east coast and linear increases along the west coast.

But it won’t take a storm to see images like the ones we’ve seen from the northeast this winter. “The area of ​​Boston that flooded in our January storm and sent dumpsters floating down the street is roughly the same area that will be chronically flooded, just with the tides, in about four decades.” , said Spanger-Siegfried.

The Union of Concerned Scientists has produced maps, unaffiliated with the NOAA report, that show areas that will be regularly hit by high tide flooding over the next few decades.
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Now is the time to prepare

Even if the most optimistic projections are used, where sea level rise continues at its current rate without accelerating – considered extremely unlikely without prompt and immediate action to reduce greenhouse gas emissions – Flooding at high tide will remain a major problem in some of the country’s largest cities.

New York, under the low scenario, still projects 130 days of high tide flooding per year by the end of this century, while Miami and San Francisco would see 60 and 30 days per year, respectively.

Projected annual high tide flood frequencies for major cities based on different global sea level rise scenarios.

With this report, Sweet and his team at NOAA’s National Ocean Service hope to inform coastal community managers and policy makers of the significant and imminent threat they face from rising seas.

“Understanding the risk to communities from relative sea level rise is important in mitigating and preparing for the impacts of flooding,” Sweet said.

But now is the time to prepare, and some cities such as Norfolk, Virginia, Miami Beach, Florida and Charleston, South Carolina, which already experience sunny flooding a few days a year, are planning or implementing engineering solutions in large scale. to cope with sea level rise.

But there are still ways we can all help “steal the tide.”

“There are real differences in the floods that are projected under different scenarios of future sea level rise,” according to Spanger-Siegfried.

“By reducing global warming emissions and slowing the rate at which sea level rise is accelerating, we can buy time to adapt to the change that is already underway.”

CNN meteorologist Judson Jones contributed to this story.

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