Federal report: high-tide flooding could occur ‘every other day’ by the end of this century

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Flooding at high tide, which can wash water onto roads and inundate homes and businesses, is an occasional occurrence in coastal areas. But its frequency has rapidly increased in recent years due to rising sea levels. Not just during storms, but also increasingly on sunny days.

Years ago, the late Margaret Davidson, director of coastal programs at the National Oceanic and Atmospheric Administration, warned that it wouldn’t be long before such flooding became routine. “Today’s flood will become tomorrow’s high tide,” she said.

A new NOAA report has released startling new projections that back up Davidson’s warning.

By 2100, according to the report, “high tide flooding will occur ‘every other day’ (182 days/year) or more often”, even in a ‘low intermediate scenario’ in coastal areas along the East Coast and Gulf of Mexico. This scenario works under the assumption that emissions of greenhouse gases – which warm the climate and accelerate sea level rise – are reduced.

For a more aggressive “intermediate” scenario, in which greenhouse gas emissions continue at the current rate, high tide flooding is expected to occur 365 days a year.

Sea level rise and coastal flooding are already accelerating

In February, scientists published a separate study concluding that they had already detected an acceleration in sea level rise and that it is expected to accelerate further in the coming decades as the ice sheets disintegrate. and ocean waters expand.

The implications of sea level rise on high tide flooding are already apparent on the ground.

William Sweet, lead author of the NOAA report, witnessed an increase in flooding firsthand. “I moved to Annapolis last year,” he said in an interview. “Since I moved there, I’ve seen six or seven days when the water has reached the windows. What we’re seeing is that along the east coast and mid-Atlantic, in particular, flooding is already accelerating.

In 15 years, the incidence of high tide flooding in the mid-Atlantic has doubled from an average of three days per year in 2000 to six in 2015, according to the NOAA report.

“It’s a very important result,” Sweet said. “What this means is that the change is not a gradual linear change, but measured in leaps and bounds. By the time you realize there is a flood problem, the impacts will become chronic quite quickly. .

A similar acceleration in coastal flooding has been seen in other locations along the Eastern Seaboard, including Florida, the Carolinas and the Northeast.

Virtually every time the tides are intensified by the lunar cycle in South Florida, media reports show flooding due to “sunny weather flooding,” which only a few decades ago rarely occurred.

The royal supermoon peak tide offers a glimpse of sea level rise along the east coast

Last winter, Boston saw its highest and third-highest tides in recorded history as northeasters beat southern New England in January and March.

“The record-breaking January 2018 event would not have broken the record were it not for the relative sea level rise that lifted the tide and storm surge above the level reached in 1978,” said Andrew Kemp , assistant professor of land and ocean. sciences at Tufts University, told the Boston Globe.

Future projections are “crazy”

The prospect of high tide floods occurring every day or even every other day at the end of this century is hard to imagine.

Michael Lowry, a visiting scholar at the University Corporation for Atmospheric Research, expressed his shock on Twitter after seeing these projections. “It’s hard to overstate the importance of this,” he said. “It’s not even the high, high, or extreme mid-scenarios that bring us 365 [days per year] high tide in my lifetime. It’s crazy.”

Even by 2050, the report predicts that high tide flooding will occur between 50 and 250 days a year along the East Coast, depending on the emissions scenario.

“It’s so huge” tweeted Alan Gerard, division chief at the National Severe Storms Laboratory. “And even the increase by 2040. It’s not that far.”

The impacts are “huge”

Astrid Caldas is a senior climatologist at the Union of Concerned Scientists who tracks the effects of rising sea levels on the coast and is extremely concerned about the predicted increase in flooding.

“By mid-century, the frequency of these kinds of ‘minor’ floods would become so disruptive that the status quo would be virtually impossible without significant adaptation measures,” Caldas said. “Without planning for floods with measures like flood protection, elevation, water management, or even moving things out of the way, the impacts on cities, their economy, and their people would be immense.”

She added: ‘Just imagine seeing streets (and properties) flooded every other day. This gives a whole new meaning to the term “harmful flooding”. Or in fact, it completely obliterates the concept, as flooding would become much more than a nuisance, but quite a serious problem requiring significant resources and innovative policies.

NOAA’s Sweet said informing policymakers and planners of escalating flood risk was the impetus for the report. Floodwaters “rising to the storefronts of Annapolis are becoming the new tide” at the end of this century, he said. “When you project this far, the assumption is that society will adapt. That’s the real reason we’re doing this: to inform decision-making so that the best science is available to plan accordingly.”

In Washington, planners pay attention

In the Washington area, major infrastructure is at risk from rising seas, including assets around the Mall, the Southwest Waterfront, Old Town Alexandria and Annapolis.

To respond to this risk, an interagency team known as the District of Columbia Silver Jackets was formed in 2014. It includes members from regional and federal agencies, such as the DC government, US Army Corps of Engineers, the National Park Service and the National Weather Service, as well as academia.

The team hosted a flood summit in 2016, developed an online flood mapping tool, and conducted a study of vulnerable neighborhoods along Watts Branch, a tributary of the Anacostia River.

“While our team has made great strides in identifying and helping to mitigate flood risks in the region, there is still much work to be done, including taking a more comprehensive, integrated and regional approach to risk management. flood,” said the Silver Jackets team. said in a statement. “The statistics contained in this report are staggering and truly highlight the fact that time is running out as we plan for the future and take action now to ensure that our country’s resources and treasures are not harmed by the floods.”

Caldas stressed that global action is needed in addition to local measures to reduce the risk of flooding at high tide. “Adhere to the commitments of the Paris [climate] The deal is hugely important, because emissions over the next two decades, through the middle of the century, will determine how much sea level rise we’ll see at the end of the century – and how much tidal flooding we’ll see. we’ll see: every other day or every day,” she said.

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