Hoboken, N.J., May 29, 2025 — During the final week of summer in 2021, Hurricane Ida emerged from the Gulf of Mexico, turned almost directly northeast and swept through the South en route to Pennsylvania, New York, New Jersey and Connecticut.
Fueled by unusually heavy rains, falling on ground still saturated by two other recent large storms, Ida would eventually carve a path of destruction through the region. Some New Jersey cities and towns received as many as nine inches of rain within a 24-hour period, overwhelming drainage capabilities; the metro region's subways, train stations and tracks flooded for days, paralyzing mass transit.
All told, Ida would wreak an estimated $75 billion in total damages and be responsible for 112 fatalities — including 32 in New Jersey and 16 in New York state.
Yet the hurricane could have been even worse in the Big Apple.
That's the conclusion of Stevens professor and Davidson Lab researcher Philip Orton , working with doctoral candidate Shima Kasaei and two U.S. Geological Survey (USGS) researchers, who recently published new simulations of that hurricane in a major journal.
These types of simulations and models are extremely valuable to agencies and community officials for advance emergency planning and extreme-event response.
"Parts of the city, including the area around JFK airport that we studied, were spared the very worst," notes Orton, an extreme-weather and sea-level modeling expert.
"If the storm's track were shifted just 30 miles eastward it would have still soaked the urban centers of New Jersey but produced far more rainfall, higher waters, stronger floods and — one can assume — additional casualties and property damage in New York City."
A fuller picture, a best case — and a worst case
To investigate the unusual nature of Ida and the ways it could have played out differently, the team first tweaked — then put to work — a respected modeling system used for forecasting regional coastal storm impacts.
USGS researchers at the Woods Hole Coastal and Marine Science Center in Woods Hole, Massachusetts, developed and first unveiled the system, known as COAWST (for Coupled Ocean-Atmosphere-Waves-Sediment Transport) in 2010.
"As the name indicates, COAWST integrates four of the most important storm factors and forces into a single model," says Orton. "No other model combines data and simulations for ocean tides, rainfall, wave heights and surge, as well as sand and sediment movement."
But even this complex model didn't capture all important factors.
In particular, coastal hazard models rarely incorporated the effect of "pluvial flooding": the kind that occurs when heavy rain falls directly onto a land surface, then runs off. In urban areas, rainfall and runoff can quickly accumulate and deepen atop streets and in low-lying areas.
"The combined effect of simultaneous high tides, storm surges, rising rivers, heavy rain and surface overflow is known as 'compound flooding.' It's particularly dangerous — but also difficult to forecast, because of all the variables involved," explains Orton.
To simulate the pluvial effect, the research group improved parts of COAWST, integrating the rainfall water volume directly into the model's primary equations and resulting floodwater depths.
The researchers then zeroed in on the Jamaica Bay area of Long Island, in New York — a highly populated area, susceptible to both coastal flooding and rainfall flooding, thus a useful location for applying the new model to help improve forecasting and emergency management — to apply the model in a test of its potential for the city's worst-ever rain event.
The result: The first flood map of Ida to be released to the public, covering one highly populated urban watershed with over 2 million residents.
In an additional sensitivity analysis, the team then simulated shifting the prevailing track of the storm both east (which would have led to higher rain intensities within the flood model's area, given the storm track) and also north, which would be expected to produce lower rain rates.
Indeed, the model showed the storm could have been much better (or worse) for New York City's neighborhoods of southern Queens and South Brooklyn. As a baseline, the newly tuned model shows that 8.8 square miles and 4621 buildings were affected by flooding greater than one foot deep.
That's bad, but shifting the parameters proved even more dramatic.
"During the worst-case scenario, a more easterly storm track, the entire Jamaica Bay watershed area experiences an extreme hourly rain intensity and an average of about 9 inches of rain (24 cm) during the storm," Orton says. "As a result, the area of deep flooding expanded to 24 square miles and 5907 buildings."
In the best-case scenario, however, the watershed could have potentially experienced 60% less total rainfall, more like 2.5 inches on average — a more common heavy-rain event that would have been far better handled by systems and infrastructure.
The researchers also simulated various alternative tidal conditions, since Ida's worst surge actually occurred during relatively low and falling tides. The results showed a high tide could have slightly increased flooding for certain areas, such as the east and west shores of Jamaica Bay and Hamilton Beach.
"These findings underscore the model's utility in representing compound flooding events, such as for hurricanes that our group has recently shown can bring both extreme rainfall and storm surge," Orton says. "Capturing that compounding effect is particularly important, given that compound floods are expected to become more common and important as sea levels continue to rise."
The team's findings were reported in the leading journal Hydrology and Earth System Sciences [Vol. 29, Issue 8: 2043-2058] in late April.
About Stevens Institute of Technology
Stevens Institute of Technology is a premier, private research university in Hoboken, New Jersey. Since 1870, technological innovation has been the hallmark and legacy of Stevens' education and research programs. Within the university's three schools, nearly 9,000 undergraduate and graduate students collaborate closely with faculty in an interdisciplinary, student-centric, entrepreneurial environment. Academic and research programs spanning business, computing, engineering, the arts and other fields actively advance the frontiers of science and leverage technology to confront global challenges. Stevens is consistently ranked among the nation's elite universities for return on investment for students, career services programs and mid-career salaries of alumni.
