A study by researchers at North Carolina State University and UNC-Chapel Hill found that coastal flooding is happening more often than expected in North Carolina.
That's because the most widely used predictor for flooding is tide gauges. Scientists have increasingly used tools like the National Oceanic and Atmospheric Administration’s (NOAA) high-tide flood (HTF) threshold to monitor tide elevation and determine regional flooding risks as a result.
But, the study’s co-authors, UNC assistant professor of city and regional planning Miyuki Hino and N.C. State assistant professor of coastal engineering Katherine Anarde, found these gauges don't account for other flooding factors that appear on land — like rain, groundwater, and local infrastructure.
"They're designed to measure the tides or water levels of oceans and bays, and that means it's imperfect or not intended to actually capture flooding on land," Anarde said. "So, while they are our best guess, we've known for a long time that they're not telling the whole story in terms of flooding."
Instead, the study used custom sensors, placed in stormwater drains and alongside roads, to measure how often — and how long — flooding occurred in three coastal towns. Over a year, the sensors tracked 26 days of flooding in Beaufort, 65 in Carolina Beach, and 128 in Sea Level.
Meanwhile, NOAA’s HTF threshold predicted only nine days of flooding in Beaufort and Sea Level and one for Carolina Beach. The tide gauges also couldn't accurately predict how long the floods lasted.
Hino said she hopes their study encourages other scientists to collect the same type of data where they live — and that might go missing otherwise.
"I think that that's one way for scientists to contribute to public safety and broader public awareness of the risks and the impacts that are being experienced right now for the general public," she said. "I think that (the numbers) show that this is a very urgent problem, and that if you're a state or federal decision-maker in transportation or planning, there's a big difference between a certain area flooding twice a year and flooding 100 times a year."
Anarde and Hino are continuing to collect data beyond the study themselves. They're working with a growing group of communities to help them find and implement solutions to flooding in their area.
"(We want to) provide that evidence so that when communities are thinking about, what are we going to invest in, what project, what grants are we going to look for, that they're directing all of that energy towards something that is really going to work," Hino said.
However, with several federal grants funding them, Hino also considers this work to be at risk.
"We are worried about the ability to continue doing this, but we have made commitments to our community partners," she said. "We are very invested in continuing to support them as they figure out how they're going to tackle these problems. So, we're doing everything we can to keep things running."
"Our data highlight that the problem of sea level rise is not for future generations, it's a now problem," Anarde added. "So any support for these sorts of monitoring programs are essential, not just for planning for the future, but daily decisions made by coastal residents on whether or not it is safe to leave their home."
