Rise in Flooding Frequency Means New, Land-Based Sensors Might be Needed
NC State researchers contributed to a recent paper that investigates a new way to track ‘sunny day’ flooding events, which could help our state’s coastal communities better respond to sudden storms.
These days, the average summer rainstorm can wreak havoc on communities — especially those in coastal or low-lying regions.
“We’re now seeing flooding in coastal areas outside of extreme storms like hurricanes,” says Katherine Anarde, an assistant professor of coastal engineering at NC State University.
It’s a phenomenon researchers call “sunny day” flooding. And it’s become much more common than prior models estimated.
“It’s flooding a lot more on land than we previously thought, and it’s impacting people’s daily routines,” Anarde recently told WRAL News.
Anarde is one of many NC State researchers working on the Sunny Day Flooding Project, which spans several disciplines and institutions. Our university is one of three UNC System schools — joined by the University of North Carolina at Chapel Hill and UNC Wilmington — involved in the research project, which also includes researchers from Arizona State University; the University of Hawai‘i at Mānoa; the Museum of Life and Science, located in Durham, North Carolina; and Sediment LLC.
In June, the interdisciplinary research team published a peer-reviewed paper in the open-access journal Nature Communications Earth & Environment. Titled “Land-based Sensors Reveal High Frequency of Coastal Flooding,” their paper reported findings from one year’s worth of data collected by the Sunny Day Flooding Project.
Last week, researchers from the Sunny Day Flooding Project told the Carolina Beach town council that its streets had seen saltwater for a total of over two full months in the past year.
Using sensors placed in storm drains, the Sunny Day research team detected flooding on 65 days in Carolina Beach. Meanwhile, about a 150-mile drive north, in the unincorporated community of Sea Level, the sensors detected flooding on 128 days — more than a third of the entire year.
The two widely accepted figures used to infer flooding on land are the National Oceanic and Atmospheric Administration (NOAA) High Tide Flooding threshold (HTF) and the National Weather Service’s minor flood threshold (NWS), which are both based on tide gauge data.
“In general, the thresholds drastically underestimated the number of floods,” Anarde says.
Anarde says that the HTF and NWS tide-gauge-based estimates “were very different” from the numbers that the team’s custom flood sensors detected over the course of the study period.
“In addition to being inaccurate in terms of how often it is flooding, our findings also show that the actual duration of the floods is longer than is captured by the HTF and NWF thresholds,” says Miyuki Hino, corresponding author of the recently published paper and an assistant professor of city and regional planning at UNC-Chapel Hill. “Essentially, the thresholds don’t adequately account for how long it takes water to drain off of land.”
Anarde says their research shows that land-based measures of flooding are needed to better inform future policy and planning decisions.
“There can be flooding during everyday rain showers or at high tide on sunny days. It’s important that the methodology we use to monitor and predict flooding reflects this reality, since sea-level rise means these flooding events are going to become even more common,” Anarde says.
Anarde and Hino are continuing to partner with affected communities to identify and evaluate response strategies that can mitigate the impacts of chronic flooding.
This article is based on a news release from NC State University.
