The US East and Gulf Coasts will experience greater—but different—storm surges as global warming progresses, according to a new study.

The two regions differ in how ocean and atmospheric circulation and sea level interact to produce storm surges, researchers say. The study is the first to compare how different parts of the Atlantic Coast might fare during storms. Scientists examined the effects of both tropical cyclones, including hurricanes, and extra-tropical cyclones, such as nor’easters.

The team used a new global climate computer model that allowed them to combine information on weather, climate, and sea level in a fully integrated way.

The findings show that even in the absence of global warming, the Gulf Coast, and especially New Orleans, is particularly vulnerable to storm surge. As the climate warms, the area will become even more susceptible to extreme storm surges, says first author Jianjun Yin, an associate professor of geosciences at the University of Arizona.

Storm surge factors

More than 60 million people live in the Atlantic and Gulf of Mexico regions. Between 2000 and 2017, 13 hurricanes hit those regions, each causing more than $10 billion in damages.

For both regions, storm surge heights will increase in the future as warming progresses, Yin and his colleagues found. Stronger hurricanes will affect the Gulf Coast and increased sea level will affect the East Coast.

“For the Gulf of Mexico coast, the extreme sea level is highly sensitive to tropical cyclone characteristics like the storm winds. So if the hurricane becomes stronger, there’s an elevated storm surge height because the region is highly sensitive to the storm’s winds,” Yin says.

“But for the East Coast of the US, especially the Northeast coast of the US, the story is different—the maximum storm surge is mainly influenced by the background sea level rise,” he says.

Extreme events

Yin had done previous research on sea level rise using computer climate models and wanted to investigate what scientists call “extreme sea level events”—big spikes in daily coastal sea level, generally caused by storms.

However, previous models couldn’t handle the complex interactions between the ocean and the atmosphere Yin wanted to include, either because the models lacked an integrated approach or were too coarse.

Technology, in the form of a new global climate model developed by the NOAA Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, came to the rescue.

Using the new model, GFDL CM4, allowed Yin and colleagues to incorporate information about tropical and extra-tropical cyclones, atmospheric and oceanic circulation, weather, and sea level rise. Having such rich information in the model allowed the team to more accurately predict how the seas along the eastern seaboard of the US would respond to storms.

The team studied the coastline from Halifax, Nova Scotia, to Houston, Texas.

Storm surges and CO₂

The researchers used the model to analyze several simulations. The control used pre-industrial conditions similar to those in the 1800s. Another simulation added more and more CO₂ into the model’s atmosphere at a rate of increase similar to that observed since the mid-20th century.

The pre-industrial control simulation revealed the underlying differences driving storm surge in the two regions—wind strength along the Gulf Coast and sea level along the East Coast.

The simulation that added CO₂ into the atmosphere year after year projected that as warming progresses, there will be fewer—but stronger—tropical cyclones.

“For the CO₂ experiment, we found that the elevated storm surge is influenced by different factors on the East Coast than the Gulf Coast,” Yin says.

In addition, as CO₂ in the atmosphere increases, the model reveals that the Atlantic Ocean’s Atlantic Meridional Overturning Circulation will slow down, exacerbating sea level rise and storm surge on the East Coast.

“AMOC transports a lot of heat northward. It’s mainly responsible for the mild climate over Europe,” Yin says. “If AMOC slows down, it can influence the weather and climate over Europe and North America and cause regional sea level rise.”

The paper appears in the Journal of Climate. Additional coauthors are from the National Oceanic and Atmospheric Administration, Princeton University, the University of Oxford, and New York University.

NOAA and the National Science Foundation funded the work.

Source: University of Arizona

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