New York City came to a standstill on Friday as flooding closed roads and subways and inundated schools in one of the major storm-related emergencies since the remains of Hurricane Ida hit in 2021.
It is not a problem unique to New York. Flood risk is increasing across the United States with worsening climate disasters and increasing pressure on aging infrastructure.
“The water has nowhere to go”
What should a flood-proof city look like? The edge asked Samuel Brody, director of the Institute for a Disaster Resilient Texas and professor in the Department of Marine and Coastal Environmental Sciences at Texas A&M University in Galveston.
This interview has been lightly edited for length and clarity.
Are cities especially vulnerable to flooding? And if so, how?
Absolutely. Cities have more impervious surfaces and are expanding outward with roads, rooftops and parking lots. The water has nowhere to go but downstream and sometimes into people’s homes and businesses.
One of the trends we’re seeing across the country is that flooding is happening in places we never thought it would, and that’s because of the role the human-built environment plays in exacerbating and sometimes completely creating these floods. Some of that is playing out in New York City today. If you read the newspaper any given week, you will see some type of flooding in a developed area somewhere in the United States.
Therefore, it becomes very important for cities to think about their drainage infrastructure, and not only establish effective and adequately sized drainage infrastructure, but monitor, maintain, renew and update those systems over time. Historically, in the United States we have done a very poor job of this.
That caught my attention in the report You and other researchers published in 2018 that found that “Many of the urban wastewater and stormwater systems that provide the backbone of urban flood mitigation are in poor condition.” How did that happen?
In Houston where I live, let’s say the stormwater system was installed in the 1950s. Well, all the development that has happened since then is putting more volume and velocity of water into that system so that the system is just below of its capacity.
Even the systems that are designed today are only designed for, say, a five-year storm. In the United States, the risk baseline is a 100-year event. A 100-year event has a 1 percent chance, in any given year, that an area will be inundated by floods. That doesn’t mean you have a 100-year storm and then feel like you’ll be safe for another 100 years. It simply means that each year there is a 1 percent chance.
New York City and most major cities are under-engineered because it would be too expensive to allow a storm sewer system to handle a 100-year event. But that’s what we’re seeing. New York has received about one, possibly two inches of rain per hour today. A 100-year storm in New York City is about 3.5 inches per hour. That’s not even close to a 100-year event, but everyone is flooding because the storm drain system is old and under capacity. There is not enough money to keep it up to date and accommodate the expanding development taking place. We are just beginning to see some of the impacts of climate change, resulting in more intense rainfall events in many places.
How is flood risk changing with climate change? New York City Department of Environmental Protection Commissioner Rohit Aggarwala said at a press conference today: “The sad reality is that our climate is changing faster than our infrastructure can respond.”
That may be true, but I would challenge that claim by saying that a much faster and more powerful vector of risk, in that case, is that human development is changing much more rapidly than our drainage systems and infrastructure can accommodate; climate change, which is real, which is fundamental, which is happening.
The man-made environment has been a problem observed for decades. And I think to ignore this as the root cause of the problem right now would be missing the whole picture. What is overwhelming our infrastructure right now is more our development decisions and our overall patterns of human impact on the landscape than it is sea level rise and changes in rainfall patterns, which is happening, but is a variable of much longer and slower influence.
So what would a more flood-proof city look like?
There are four dimensions of what a flood-resistant city would look like. The first is to avoid, to get out of the way. It means building higher in some cases; It means moving away from vulnerable areas or letting the remaining ecological infrastructure, such as natural wetlands, do their job, acting like a sponge and not necessarily covering them.
The second dimension is to accommodate. There are some places where we want to let it flood. Either by creating retention and detention areas or, again, leaving these natural wetlands alone. We are so used to fighting against water. Accommodation and living with water and understanding that in these landscapes, both urban and non-urban, there are places where we want to let it flood.
“We are so used to fighting water.”
The third component is resilience, which has to do with the history of flood management in the United States: the fight against floods. They are barriers, dikes, dikes, different ways of containing water. We know that doing that alone as our primary strategy doesn’t work over time. That’s why I mention it as a third component, not the first.
The last component is communication, which tells the story of the risk. It’s about providing information in a way that is interpretable and actionable for decision makers, but also for individual residents, so they better understand what their risk will be and can take action.
We are finding that there is such a lack of awareness and distortion of communication around flooding that people are being caught off guard. Even today, in New York City, they are surprised.
Authorities have said this is the wettest day in New York City since Hurricane Ida hit in 2021. Flooding then killed more than a dozen people in basement apartments, many of whom were low-income immigrants. What could make certain sectors of a city more vulnerable than others? And what can be done to solve these disparities?
Basement flooding is a big problem in Houston, which is the epicenter of urban flooding in the country. The rich houses are the ones that are very elevated and have all kinds of expensive systems to resist flooding.
One of the problems with our American system of flood risk reduction and management is that it tends to favor wealthy populations. More expensive plots tend to be less prone to flooding. More expensive structures and homes are better able to cope with flooding. Low-income neighborhoods tend to have fewer drainage resources.
This is in contrast to other countries such as the Netherlands, where they set a precedent by protecting the socially vulnerable first. It’s not just income: it’s age, education; those are the populations that need to be protected first.
