Everyone knows that flooding is a problem. We see images of submerged streets, overwhelmed subways, and homes surrounded by water. But what many of us don’t know is that there are different types of flooding, each with its own causes, impacts, and risks. If we want to better prepare for the next big storm, or even the next heavy rainfall, learning about this helps us understand what we’re up against.
Tidal flooding happens when high tides push seawater onto low-lying roads or shorelines. It doesn’t take a storm to cause this, just the normal pull of the moon and a higher-than-usual tide. With sea levels rising due to climate change, this type of flooding is becoming more frequent in places like Hoboken, NJ, and Lower Manhattan. According to the National Oceanic and Atmospheric Administration (NOAA), the frequency of high tide flooding has more than doubled since 2000 in many East Coast cities.
Coastal flooding happens during storms when strong winds and low-pressure push ocean water inland in a surge. One of the worst examples was Superstorm Sandy in 2012, when a record-breaking storm surge of over 14 feet inundated New York City and the New Jersey coast. It has been reported that Sandy caused over $50 billion in damages and displaced thousands of residents across the U.S.
River flooding occurs when heavy rainfall overwhelms rivers and streams. This can be gradual or fast, depending on the soil, terrain, and rainfall intensity. In fact, the U.S. Geological Survey (USGS) reports that the remnants of Hurricane Ida in 2021 dropped over 7 inches of rain in parts of the New York metro area, causing the Bronx River to overflow and flood nearby homes and streets.
Flash flooding is more sudden. It happens when rain falls so rapidly that water can’t drain away quickly enough, especially in paved cities and with an outdated sewer system. A report from the NYC Mayor’s Office of Management and Budget highlighted that, during Ida, flash floods damaged ground floor spaces, destroyed mechanical equipment, and tragically killed people who were trapped in basement apartments.
Stormwater Flooding occurs when rain overwhelms the combined sewer system, causing water to back up into streets, subway stations, and basements. This stormwater flooding is increasingly common, especially during summer thunderstorms. According to the NYC Department of Environmental Protection, about 60 percent of NYC uses a combined sewer system to convey stormwater runoff and about 70% of NYC’s land area is covered by impervious surfaces, which generate a significant amount of stormwater runoff. It is clear that stormwater capacity in many neighborhoods of NYC hasn’t kept pace with the intensity of recent storms and those projected in the future.
Groundwater flooding happens when the water table rises above the ground surface after prolonged rainfall. It’s difficult to manage because it doesn’t flow like surface water; it leaks through soil and into buildings. It is reported that, in areas like Southeast Queens, the groundwater table has risen approximately 40 feet since the 1970s, which has made groundwater issues more severe. This has led to widespread property damage, health hazards, and financially burdened homeowners.
But wait, there’s more…
Compound flooding occurs when several flood types hit at the same time, which results in the most dangerous floods. This can happen when there’s a storm surge during high tide combined with heavy rainfall and backed-up sewers. The rain has nowhere to drain because the tide is already high, and the surge is blocking river outlets from emptying into the sea. All these water sources (rainfall, river water, and coastal surge) combine to create a much worse flood than any one of them would alone. As explained by flood modelers, it’s not just about how much water there is, but how different sources of water interact in time and space, overwhelming both natural and built drainage systems. This leads to catastrophic results. Sandy is one example, but compound events are becoming more common with climate change.
Similar to last year’s Atlantic hurricane season, NOAA projects an above-normal season for this year, with up to 19 named storms and 10 hurricanes, including 3-5 major hurricanes (Category 3 or higher). With risks rising every year, flooding is no longer rare or predictable. It’s not just possible; it’s likely. Everyone can confirm that it’s happening more often, in more places, and in more dangerous ways.
The first step toward protecting ourselves and our communities is understanding the risks. Knowing how flooding happens helps us prepare smarter, respond faster, and recover stronger.
If this article helps you better understand flooding, share it with someone in your circle. Awareness is the first step toward resilience!
