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Preparing for extreme sea levels is different depending on location and time, new study finds
/ Categories: Climate, Marine Science

Preparing for extreme sea levels is different depending on location and time, new study finds

Sometimes to understand the present, it takes looking to the past. That’s the approach coastal researchers, supported by the NOAA Climate Program Office Climate Observations and Monitoring (COM) Program, are taking to pinpoint the causes of extreme sea level changes.

Using historical data from tide gauges that line U.S. coasts, University of Central Florida (UCF) researchers created an extreme sea level indicator that identifies how much of a role different major weather and ocean forces have played in affecting extreme sea levels in coastal areas around the country.

They published their latest findings today in the journal Nature Scientific Data.

Thomas Wahl and Mamunur Rashid, study authors

Thomas Wahl and Mamunur Rashid, study authors

CPO-funded coastal researchers Thomas Wahl and Mamunur Rashid (University of Central Florida) display data from their extreme sea level indicator study. Photo credit: Karen Norum, University of Central Florida, Office of Research.

The researchers hope that further development of the indicator may one day allow scientists to predict when and where extreme sea level changes will occur. Indicators are measures that can quantitatively describe situations—in this case sea level rise.

“What this indicator does, which other indicators do not show, is how weather and climate interact with predictable tides to make up high sea levels that can be potentially dangerous,” said Thomas Wahl, NOAA COM Program-funded co-author and assistant professor in UCF’s Department of Civil, Environmental, and Construction Engineering and National Center for Integrated Coastal Research.

“Knowing such allows for heightened awareness for planners in charge of 'low-risk, high-consequence' decisions and infrastructure when such weather and climate patterns are predicted to occur,” added Dr. William Sweet, NOAA Oceanographer and study co-author. “It complements our NOAA high tide flood outlooks that provide next-year and multi-decadal guidance to planners about more routine flooding now occurring within many coastal communities.”

Extreme sea level change, in the context of this study, is when the likelihood for water level thresholds to be exceeded is higher or lower than under normal conditions, taking into account the current increase in average sea level.

Extreme sea level rise can have a devastating effect on coastlines, where 40 percent of the U.S. population lives, or more than 126 million people.

The contributing factors behind extreme sea levels that the researchers examined were average annual sea level, low frequency tides, and storm surges. 

Average annual sea levels change and can be affected by forces like the El Niño–Southern Oscillation. Low frequency tides have higher water levels and occur less often than average tides, and storm surges, occurring from hurricanes or nor-easters, also impact sea levels. 

“This indicator illuminates the fact that it's not just sea level rise that increases coastal flood risk.  There are weather patterns and long-period tide cycles that can align and compound flood risks,” Dr. Sweet said. “As sea levels continue to rise and coastal communities continue to flood more often, every inch matters.”

Houston Sunny Day Flooding

Houston Sunny Day Flooding

Sunny day flooding in Houston, TX

For Florida’s Gulf Coast, average sea level and storm surges have been the most responsible for creating periods where extreme sea level events tended to be higher or more frequent, the indicator shows. 

This is in stark contrast to the North Atlantic coast, such as Portland, Maine, where low frequency tides have had a greater influence on extreme sea levels than variations in average sea level or storm surges, especially in the summer.

Knowing these differences can also aid policy makers in devising coastal resiliency strategies, said Mamunur Rashid, a postdoctoral research associate in UCF’s Department of Civil, Environmental, and Construction Engineering and National Center for Integrated Coastal Research and the study’s lead author.

“Hopefully, at some point such information can help guide the development of sustainable coastal adaptation plans,” Rashid said.

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