What can the city look like after a flood? A four-dimensional study of what flood-resilient cities can look like in the United States

New York City came to a grinding halt Friday as floods shut down roads and subways and inundated schools in one of the biggest storm-related emergencies since the remnants of Hurricane Ida hit in 2021.

One of the trends we see is that flooding is happening in places we never thought would happen, and that is because of the role the human- built environment has in creating these flooding events. New York City is a place where that is playing out today. If you look in the paper any given week, you’re going to see some kind of flood event in a developed area somewhere in the United States.

How should the city look after a flood? The institute for a disaster resilient Texas is headed by the director and the professor at Texas A&M University at Galveston is in the department of marine and coastal environmental science.

Absolutely. Cities have more impervious surfaces and are sprawling outward with roadways, rooftops, and parking lots. The water has nowhere to go but downstream and sometimes into people’s homes and businesses.

So it becomes very important for cities to think about their drainage infrastructure, and not just put appropriate size and effective drainage infrastructure in place, but monitor, maintain, renew, update those systems over time. That has not been a good job of that in the United States.

Even the systems that are designed today, they’re only designed for, for example, a five-year storm event. In the United States, the baseline of risk is a 100-year event. A 1% chance is what a 100 year event is, in any given year. That doesn’t mean you get a storm in 100 years. and then you can feel like you’ll be safe for another 100 years. It doesn’t mean that there’s a 1 percent chance.

That may be true, but I would challenge that statement by saying a much quicker, more powerful vector of risk, in that case, is that human development is changing much more quickly than our drainage systems and our infrastructure can accommodate — much more quickly than climate change, which is real, which is fundamental, which is happening.

There are four dimensions of what would be a flood-resilient city. Getting out of the way is the first thing. It means building higher in some cases; it means pulling away from vulnerable areas or letting remaining ecological infrastructure like naturally occurring wetlands do their job, act as a sponge, and not necessarily pave them over.

The second dimensions are designed to accommodate. There are places where we want to let it flood. Allowing the naturally occurring wetlands alone, whether that is creating areas of retention and detention or not is what it is. We have a lot of experience fighting water. Living with water in these landscapes is a matter of living in places where we want to let it flood.

The third component is resistance, which is all about the history of flood management in the United States: fighting the flood. There are different ways to hold the water back. We know that doing that alone as our main strategy doesn’t work over time. That’s why I’m mentioning that as a third component, not the first.

The last component is communication, telling the story of risk. It gives information that is actionable to those decision-makers, but also to individual residents, to help them understand what their risk is so that they can take action.

One of the problems with our system in the US of flood risk reduction and management is that it tends to favor wealthy populations. More expensive parcels tend to be less flood-prone. Households and expensive structures have the ability to deal with flood waters. Lower-income neighborhoods tend to have fewer drainage resources.

The Netherlands put a precedent on protecting the socially vulnerable first. Those who need to be protected first are the age, education and income groups.

Urban stormwater infrastructure in the past and the present: From sewers and canals to rain gardens and rain gardens in NYC, Los Angeles, and other cities

On a warming planet it will rain more and storms will get more intense. This pain will be especially acute in urban areas, which are built on stormwater infrastructure designed to handle the rainfall of yesteryear. Think back to what the builders of the last century wanted: sewers and canals that funneled rainwater as quickly as possible into a river, lake, or ocean, before it had a chance to accumulate. That worked fine, most of the time. The number of catastrophic flooding has grown over the intervening years. The ancient wastewater systems are tasked with getting rid of large amounts of water.

Likewise, Los Angeles is deploying rain gardens, as well as directing rainwater into spreading grounds—basically, big dirt bowls where water trickles underground. The amount of water that goes back into the soil will be used to replenish the available water in the American West.

Green spaces are not inexpensive because of the high cost of urban land. Where it’s not possible to plant the landscape, cities like NYC are deploying permeable pavement. Instead of acting as a barrier for stormwater, these surfaces let rain soak into the underlying dirt. Some cities are also starting to charge water customers additional stormwater fees, using satellite images to determine how permeable a property is and charging if there’s a lot of pavement instead of vegetation.

The city of the future may be spongier in ways that are obviously verdant or more subtle. If they are more enjoyable as the planet warms, the rains of the future may be a bounty, not a burden.