Coastal flooding occurs at predictable times, research reveals
Coastal flooding may seem unpredictable, a natural disaster that occurs randomly. But UCF researcher Ivan Haigh has found that recurrent coastal floods occur at highly predictable times.
In a recent study published in Nature Communications , Haigh and a team of international researchers show that coastal flooding tends to occur at certain times of day, reflecting the timing of the tides. While previous research has largely focused on the seasonal timing of river and coastal flooding, this is the first study to show that floods with impacts have predictable daily timing across regions.
"Floods have traditionally been viewed as primarily weather-driven and therefore relatively unpredictable in their exact timing," Haigh says. "But surprisingly little attention has been paid to what hour of the day flooding occurs. Another reason is the way we measure flooding. We commonly talk about the number of 'flood days' per year. Once an event is reduced to a flood day, the information about whether the flooding happened at 3 a.m., 8 a.m. or 3 p.m. disappears."
Using tide gauge data and flood event records from the U.S. and the United Kingdom, the researchers found clear patterns in when floods occur. For example, in Boston, floods occur predominantly around noon and midnight, while in Southern California, they are more common in the morning. In Florida, the timing can vary along the coastline because the tides differ from location to location. Along the Atlantic Coast and down toward the Florida Keys, coastal flooding is moderately predictable, but along the Gulf Coast, flooding is less predictable.
Tides set the flood clock
Haigh says tides largely determine that predictability.
"In many locations, tides determine whether storm surge is sufficient to push water levels above flood thresholds," Haigh says. "As a result, even storm-driven flooding often inherits the timing of the tides."
The researchers also found that this phenomenon isn't unique to locations that experience semidiurnal tides, which consist of two high tides and two low tides each day. It also happens in places with diurnal tidal systems, with one high tide and one low tide per day, because of the way different tidal signals interact.
Rising seas heighten the stakes
As sea levels continue to rise, Haigh says coastal flooding is increasingly occurring without storms, making his findings more significant.
"This matters because timing influences impacts," Haigh says. "The same flood can have very different consequences if it occurs during the morning commute, business hours or in the middle of the night. Understanding these temporal patterns could improve flood forecasting, emergency planning, infrastructure operations and long-term coastal adaptation."
More precise warnings for coastal communities
Haigh says this work could improve existing flood forecasts, providing more warning before disasters occur. This can help people, businesses and emergency managers anticipate disruption and plan accordingly.
This information is also likely to become more useful as sea levels rise.
"Higher mean sea levels signify that it will take only a relatively small weather contribution or sometimes simply a very high astronomical tide to cross a flood threshold," Haigh says. "Understanding exactly when those critical tidal windows occur could therefore become an increasingly important component of coastal flood forecasting and preparedness."
