As New Tropical Storm Takes Aim – Study Spotlights East Coast Flood Risk
September 28, 2015
New research out of Penn State underlines the increased risk to the US East Coast due to storms.
Meanwhile, a new tropical storm is spinning up, and perhaps taking aim at the northeast….
Flood risk for New York City and the New Jersey coast has increased significantly during the last 1,000 years due to hurricanes and accompanying storm surges, according to a study by Penn State University, Rutgers University, Massachusetts Institute of Technology, Princeton University and Tufts University.
For the first time, climate researchers compared both sea-level rise rates and storm surge heights in prehistoric and modern eras and found that the combined increases of each have raised the likelihood of a devastating 500-year flood occurring as often as every 25 years.
“A storm that occurred once in seven generations is now occurring twice in a generation,” said Benjamin Horton, a Rutgers marine and coastal sciences professor. Horton also is the principal investigator on the National Oceanic and Atmospheric Administration and National Science Foundation grants funding the research.
The study, “Increased Threat of Tropical Cyclones and Coastal Flooding During the Anthropogenic Era,” was published today in PNAS (Proceedings of the National Academy of Sciences). This study is unique because researchers combined sea-level records, hurricane and storm surge models to look at flooding in the New York City region in the two time periods – prehistoric (pre-anthropogenic, A.D. 850 to 1800) and modern (anthropogenic, 1970 – 2005).
Flooding heights increased 1.2 meters from the prehistoric era to the modern era, researchers found. “This is mainly due to the rising sea level. Sea levels have been rising in the modern era because of human activity,” Horton said. “Sea-level rise between hurricanes raises the ‘baseline’ water level and makes flooding more likely.”
Flood heights increased 1.2 meters from the prehistoric era to the modern era, mainly due to rising sea level, researchers found.
Much of the damage wreaked by Hurricane Sandy was a result of the 3-4m storm surge it caused, the study says.
When a storm weather system is over the sea, its low pressure centre pulls up the surface of the water. Then, as the storm blows onto the land, the wind pushes the sea towards the coast, creating even higher sea levels and hitting the coastline with large waves. This is a storm surge.
The height that a storm surge can reach is dependent on the underlying sea level, the tide, and scale of the tropical cyclone. So as sea levels rise, a storm surge has more chance of breaching coastal flood defences. Likewise, if tropical cyclones become more frequent, more intense or longer-lasting, storms surges could also reach new heights.
To see if either had changed, Reed and her colleagues compared coastal flooding in New York City during two time periods: a “pre-anthropogenic era” when the human influence on climate was “minimal” (the years 850 to 1800) and an “anthropogenic era” when it was “dominant” (years 1970 to 2005).
As records of tropical cyclones in the North Atlantic only stretch back to 1851, the researchers first had to reconstruct a data record of cyclones. They used data from state-of-the-art climate models for sea surface temperature, humidity, and wind speed – all important factors in how cyclones develop – to create a dataset of tropical cyclones from 850 to 2005. They could then work out the size of storm surges the cyclones would produce, and combine the information with sea level data to give flood heights across the whole 1,200-year period.
When the researchers compared the pre-anthropogenic and anthropogenic eras, they found the average height of a coastal flood hitting New York City has risen by about 1.24m since humans started affecting the climate.