The U.S. is already facing a flooding crisis as sea-level rise pushes tides ever higher. But it’s only going to get worse with flood risk doubling every five years in the coming decades, according to a new study. That means floods that used to happen once in a person’s lifetime occur every year or even every day.
The new findings, published on Thursday in the journal Scientific Reports, are based on sea-level rise projections and observational data from tide gauges at over 200 sites in the U.S. By examining the current trends in tides and storm surge (but not waves), the scientists are able to forecast how that might change over the next few decades. The team looked only at sites with at least 10 years of data.
Previous research has already concluded that most U.S. beaches may be lost as a result of higher sea levels, reducing coastal protection. That puts more than recreation at risk. Major coastal cities like Miami and vulnerable low-lying island nations could be wiped off the map.
While most studies look far into the future to mid-century or even the end of the century, the new one takes a look at how our coasts will transform much sooner than that. The study defines extreme floods as ones that have a 2 per cent chance of occurring in a given year at a given location under our current sea levels. But those levels are projected to rise in the coming decades as the planet heats up. How much they rise is largely dependent on when we cut carbon emissions.
Using a business-as-usual emissions scenario where we don’t make much effort to slow down carbon pollution, the study found that the odds of extreme flooding doubles every five years starting in 2025 in most coastal locations. That means that by 2050, we may see extreme flooding events every year. By 2100, they could very well happen every day during a regular high tide.
Even a small rise in sea level can have an exponential impact on flooding frequency. The findings show that for low-lying locations, just a centimeter increase in sea levels is all it takes to double the odds of extreme flooding. Overall, many locations will double the risk of flooding with just 10 centimeters of sea-level rise. What many cities like Miami or Honolulu experience as so-called nuisance flooding today would become the norm and make living in coastal cities a disaster.
“Those nuisance-level flood events are going to increase in their spatial extent and frequency and severity to the point where living in urban waterfront areas is going to become increasingly problematic and difficult,” study author Sean Vitousek, a research oceanographer at the U.S. Geological Survey, told Earther. “They’re going to reach elevations that make them not just nuisances anymore [but] where, essentially, probably most of the low-lying streets are just completely shut down and full of several feet of water going forward in the future.”
The study doesn’t take into account any other weather events, such as El Niño, that influence flood patterns. Nor does the study involve any climate modelling to see the ways climate change at large—through stronger storms or increased rainfall—will also impact flooding. That means things may look a lot worse.
“[The study] may only tell half the story, but if the half of the story that we are considering is only sea-level rise and not necessarily climatic stories in storminess, that part of the story in sea level rise is very significant,” Vitousek said.
We know now there’s not much time to prepare for these extreme weather events. That’s especially true for low-lying coastal areas, which may see much higher odds of this happening. The analysis found that even in a scenario where we take drastic action to reduce our emissions, the most vulnerable coasts won’t be safe.