News | July 26, 2022

New Study Points the Way to Better Flooding Forecasts

By Ethan Huang, NASA's Sea Level Change Team

Photo of a child playing in a flooded street — A child playing during a high-tide flooding event in downtown Annapolis. Photo courtesy of the City of Annapolis

The question: How can forecasting tools for coastal flooding be improved? How have the causes of coastal flooding, in particular so-called high-tide flooding, changed over time?

The answer: A new study focuses on the causes of high-tide flooding, when sea level rise combines with other factors to push water levels above a coastal flooding threshold. Minor flooding in coastal communities can bring a variety of problems, including road closures, public health concerns, and degradation of infrastructure.

This study offers ways to improve high-tide flooding forecasting tools, including better representation of its various causes, said Thomas Wahl, an assistant professor at the University of Central Florida and member of the NASA Sea Level Change Team.

Sea level rise is a well-known cause of high-tide flooding, but the role of others, such as tidal changes and storm surges, could be made clearer.

“Doing this for the entire U.S. coast, we could see where the tides or the surge component are relatively more important compared to other regions,” Wahl said.

A map showing the number of components needed to cause a high-tide flooding event on the U.S. coast. — A map showing high-tide flooding events along the coastal United States. They are represented by the number of components that caused the event as well as the season they occurred in. Image courtesy of Thomas Wahl and Sida Li

Understanding how these different processes interact, and how they affected past events, can help create better tools for looking into the future. Doing so requires careful analysis of tide gauge data.

The analysis of past flooding events, a key element of the study, was performed by lead author Sida Li, a visiting student at the University of Central Florida.

“He was really the one who conducted the entire analysis from beginning to end with guidance from others on the team,” Wahl said.

The next step was tracing the factors that contributed to these past events, creating what scientists call a “budget” of such factors.

“We are really taking these high-tide flooding events from the past and we break them apart into the different processes that contributed to a particular event at a given location,” Wahl said. That reveals how certain processes make a larger contribution in different regions and at different times of year.

Why it’s important: The team developed a database to accompany their paper that uses more than 100 tide gauges to separate each sea level process by timescale. Other scientists can use the database to better understand how these processes work together mechanistically.

A major finding from the study: Higher sea levels often mean that fewer additional factors are needed to cause coastal floods.

“Now we need fewer of these processes to work in concert to create high-tide flooding events,” Wahl said.

Such findings, and improvement of forecasting tools, will help coastal communities better prepare for the future.