Extreme storms, like Sandy or Xaver, don’t happen often, but when they do, cities need to be prepared.
That’s why researchers have developed a new method, detailed in a study published this week in Natureto determine where extreme events, such as 100-year storm floods, are most likely to occur, whether the likelihood of such extremes is changing over time, and why.
This is important information that cities can use to help place flood protection resources, such as larger levees or larger pump stations, where they are needed most.
“We don’t want to over-design and waste money building things bigger than necessary, which is very expensive,” says Thomas Wahl, study co-author and assistant professor at UCF. Department of Civil, Environmental and Construction Engineeringand member of the UCF National Center for Integrated Coastal Research.
“On the other hand, we don’t want to build things that are too small only to find 20 years later that we underestimated the design and now we have to pay more to scale our infrastructure more,” he says.
The new study analyzes storm surge trends over the past 60 years and shows that in addition to sea level rise, changes in storm surges affect the magnitude of extreme flooding along coastlines. Europeans.
However, while some locations are seeing a further increase in extreme flooding due to changes in storm surge, others are seeing a decrease.
For example, the northern coasts of Scotland are more prone to more extreme flooding, while the coasts of Spain, France, Belgium, the Netherlands, Germany and Denmark are less likely, according to the study.
“What used to be a 50-year event, is now a 30-year event in some areas,” says Wahl. “Thus, there is an almost 40% increase in the likelihood that certain extreme events may occur.”
“But in other regions, what was once a 50-year event with a 2% chance of occurring in any given year in the 1960s is now closer to a 100-year event with just 1 % chance of occurrence,” he says. . “These changes occur above sea level rise. So while some locations see a cumulative effect of sea level rise and increased storm surges, these two- there cancel each other out in other places.
For the study, the researchers incorporated historical tide gauge data, dating from 1960 to 2018, from 79 locations all along European coastlines, into a new statistical approach they developed.
The approach takes advantage of spatial dependencies in extreme events to separate large-scale changes in storm surge amplitude over time from small-scale observation errors and noise.
This allowed them to compensate for the small, noisy samples typical of tide gauge data, says Francisco Mir Calafat, lead author of the study and senior scientist at the National Center for Oceanography, Liverpool, UK.
“Our new approach allowed us to obtain estimates of changes in sea level extremes that are much more robust and less uncertain than those from traditional approaches,” says Calafat.
And by combining climate model simulations with a data-driven storm surge model developed by doctoral student and study co-author Michael Getachew Tadesse at UCF, the researchers were able to assign whether changes in storm surges were due to internal climate variability or human-induced causes. .
For example, data from the study indicated that human-induced changes, such as increased greenhouse gas emissions, increased the likelihood that the storm surge caused by Cyclone Xaver in Europe in 2013 to occur by approximately 20%.
“Our study found that changes in storms in Europe since 1960 have altered the likelihood of extreme sea level events just as much as sea level rise, and human-induced climate change is partly to blame,” says Calafat. “This is a surprising result because, prior to our paper, the prevailing view was that changes in the probability of extreme sea level events were mainly due to sea level rise, with almost no contribution changes in storm activity.”
Part of the reason is that the role of storm surges has not been easy to disentangle until this study, Wahl says.
“We have extreme events at sea level, which are getting more and more extreme, and we’ve known that for a while,” says Wahl. “And we know that sea level rise is a big factor that drives extreme sea levels higher, just because the base water level is higher. A storm like Sandy in 2012 would not have been so bad in 1920.”
“But there’s always been this open question of whether storm surge activity also changes and leads to more frequent or more intense storm surges?” he says.
Although the study analyzed coastlines in Europe, the researchers plan to expand and apply the method to examine the risk of extreme flooding in the United States and other parts of the world.
“It will be really interesting to see if better and more robust estimates give us a clearer picture of what the past can tell us about changes in storm surges that may have already occurred along the coasts of the states. United,” he said.
The work extends Wahl’s research on coastal change, including examination of nuisance flooding and a better understanding of storm surges and related factors, such as large-scale climate variability.
The study also included co-author Sarah N. Sparrow, coordinator of the Climateprediction.net program at the University of Oxford’s Online Research Centre.
The storm surge model used in the study was developed as part of Wahl’s NASA Early Career Investigator Award and continues to be developed and used in a new project supported by the Sea Level Science Team of the NASA and a project sponsored by the US National Science Foundation under the PREEVENTS program.
Wahl earned his Ph.D. in civil engineering from the University of Siegen, Germany, and joined UCF’s Department of Civil, Environmental, and Construction Engineering, part of the College of Engineering and Computer Science at the UCF, in 2017. He is also a member of the UCF. National Center for Integrated Coastal Research and Faculty Group on Sustainable Coastal Systems.