In September 2021, Hurricane Ida slammed into the eastern United States with a powerful impact that left a lasting mark. New York City was hit by unprecedented rainfall that flooded subway tunnels, basement apartments, and city streets, overwhelming the drainage systems. The destruction was immense — claiming thirteen lives and causing damages estimated between $7.5 billion and $9 billion within the city alone. The storm was a bitter reminder of the susceptibility of urban areas to extreme weather events.
What Might Have Been Much Worse
Meanwhile, new science tells an even darker tale. Researchers at the Stevens Institute of Technology, led by Dr. Philip Orton, employed sophisticated computer modeling to model different scenarios in which Hurricane Ida’s path or timing were slightly altered. Their shocking conclusion? New York City could have been far more severely flooded if the storm had coincided with high tide or tracked differently — initiating so-called compound flooding.
Learning about Compound Flooding
Compound flooding is what happens when flooding drivers come in groups, like storm surge, pluvial flooding from heavy rain, and high tides. Individually, they are risky, but together, they can inundate infrastructure in ways much more destructive than planned for.
In recreating the complicated interactions between them using the COAWST (Coupled-Ocean-Atmosphere-Wave-Sediment Transport) modeling system, scientists simulated what might happen. The increased capacity of the model to replicate heavy rainfall flooding provided new information about how urban cities such as New York City might be more vulnerable to future storms.
The Danger Beneath Our Feet
Among the most significant findings is the heightened risk of pluvial flooding — flooding due to heavy rainwater filling the ground and streets, clogging sewers. The huge urban sprawl of New York City’s pavement and concrete minimizes natural water intake, exacerbating pluvial flooding’s destructive power. When this flooding is paired with increasing water levels from storm surges and tides, the potential for devastating inundation rises extremely high.
A Wake-Up Call for Urban Resilience
This study is an urgent wake-up call for urban planners and emergency authorities. With climate change escalating storms and rising sea levels, the threat of compound flooding will continue to increase. Being able to understand these multimodal flooding situations is critical to the planning of smarter, more resilient infrastructure. Advances such as enhanced stormwater management, modernized flood defenses, and early warning systems could mean lives saved and billions of dollars saved in subsequent events.
Looking Ahead
The Hurricane Ida and New York City narrative is not only a warning but an appeal to action. As the climate crisis speeds up, cities need to get ready for storms that trigger multiple flood threats at once. The new research makes it clear that even slight variations in timing or storm paths can significantly change outcomes — underlining the need for thorough flood modeling in city development going forward.
By identifying and tackling these covert dangers, cities such as New York can more effectively protect their communities and infrastructure from the next large storm — and when catastrophe does arrive, it’s not as bad as it might otherwise have been.
