What Cities Promise

United Nations research estimates that just under 70% of the world’s population will live in cities by 2050. That’s a 15% increase from the current conditions. It means adding another 2.5 billion people to the current urban population. Not only do cities represent massive opportunities for progress, they also demand more sustainable choices. If we do not change how we design our cities, we are surely doomed

In order to have a conversation about what cities promise, we must acknowledge where they fail. Runoff from urban areas is one the top four causes of impairment in streams, estuaries and lakes. The majority of nonattainment areas, regions that violate National Ambient Air Quality Standards (NAAQS) set by the Environmental Protection Agency (EPA), are urban areas. Urban areas, in general, have higher poverty and crime rates than rural areas. Cities can isolate us and while the relationship between happiness and urban living is quite layered, it is clear that historical patterns of growth in cities do not lend themselves to a sense of place. As we all learned in 2020, cities are a hotbed for disease transmission. We sit in traffic longer; we see fewer trees and critters. What is there to love about cities?

A view from the Battery of the crowded New York City skyline.

Well, before we all pack up the wagon and move to the country, let us hope for a moment that city planners have learned some things since they planned their first city. Like most climate solutions, reinventing cities has and will take some time. But if we pull it off, cities will be the reason that we subvert the worst effects of the climate crisis.

Stormwater

Despite the fact that urban areas are notorious polluters of streams, per capita runoff in intown neighborhoods is actually lower than in suburban areas (Figure 1). It’s true that net urban runoff is higher than net suburban and rural runoff, but the population density in cities offsets that sum and makes urban development the most efficient in terms of runoff pollution. Of course, that doesn’t mean much if cities are still releasing massive quantities of polluted stormwater into streams whenever it rains. That’s where urban innovation comes into play.

Figure 1: Per bed runoff, approximated to per person runoff, for urban and suburban neighborhoods in Atlanta, GA

The issue, in a nutshell, is too much concrete. Impervious surfaces, which do not absorb rainfall and instead transfer it over the ground surface into nearby streams, make up too much of our cities. There are plenty of examples of innovative solutions that have already been implemented in cities to address concrete jungles. New Orleans is converting lots that have been vacant since Hurricane Katrina into rain gardens. Not only do the parks offer new amenities to historically underserved neighborhoods, they also provide pockets of rain retention (200,000 gallons of it!) in a sea of concrete. In planting one million trees, New York City enhanced its rainwater retention. Trees act as a catch basin when it rains and urban forests are shown to reduce annual runoff from 2 to 7 percent. Pervious pavers, which allow water to infiltrate the groundwater, are becoming increasingly common in urban areas. As cities recognize the synergy between stormwater pollution management and urban stream quality, they’re making impressive pushes to rehabilitate stream geometry. This means regrading eroded banks and installing structures like riffles in the center of the stream and toe wood on the edge to create habitat for aquatic life. Rehabilitated streams have lower rates of erosion and healthier levels of dissolved oxygen, which supports pollution breakdown and aquatic life.

Air Quality and Carbon Emissions

Low-emission development is also at the forefront of sustainable communities and takes many different forms. In Charlotte, North Carolina, the expanding light rail provides the perfect infrastructure for transit-oriented developments (TODs), which aim to provide all basic necessities - groceries, hospitals, housing, recreation, and work - within walking distance of the central transportation hub. TODs reduce greenhouse gas emissions by diversifying transportation options and making basic needs accessible. They also have smaller land use footprints and are generally less expensive to construct when compared to lower density developments. Changes in zoning laws facilitate this and other transitions to low-emission development.

The Irwin Creek Greenway is part of a network of trails in Charlotte, NC that increases biker and pedestrian access to public transportation.

For example, the first urban growth boundary was established in Portland, Oregon in the late 1970s with the goal of limiting urban sprawl and promoting infill development. Since then many other metropolitan planning organizations (MPOs) have followed suit. Urban growth boundaries establish physical limits to urban development. There are many innovative policy tools that make this possible. The first is monetarily incentivizing infill development which converts vacant parcels into new, functioning property. Greyfield and brownfield developments, properties that are vacant or contaminated with environmental hazards, are offered up to developers at a low cost in exchange for revitalization and remediation of the property. This tool refocuses development within the urban core and prevents sprawl.

Another is called transfer of development rights (TDRs). Every piece of property has a number of rights attached to it. Take, for example, a home far out in the country. The home is owned by an older couple that values the natural beauty of their land and wants to protect it from development after they have passed away. Meanwhile, a developer in town, per local zoning laws, is limited as to the number of units they can build on their property. However, if the older couple transfers their development rights to the developer and the local zoning laws permit TDRs, the developer can cash those in for higher density development in town and the property owned by the older couple is protected from development in perpetuity. What’s more, because the couple still owns the rights to the physical property they can still live on and sell their land. As such, they maintain near complete control over their land with the exception of developing it. This tool is extremely effective at creating high density developments in urban centers while simultaneously protecting existing natural resources on the outside of the urban growth boundary. You can learn more about TDRs at this link.

Serenbe Farms, a development southwest of Atlanta, GA, utilized TDRs to protect surrounding natural resources and facilitate high density development.

Urban growth boundaries, and the tools that facilitate them, are multifaceted in their benefits. Not only do they promote low-emission, high density development, they also minimize infrastructure costs associated with expanding water, sewer, and road systems into developments far from the urban core.

It is clear that per capita runoff and per capita direct emissions are minimized in cities and the reality is that the world’s population is still growing. We will have to develop; what matters is how we develop. Cities are, unequivocally, the best way to grow if we want to minimize our environmental impact. In fact, this article only scrapes the surface of what cities promise. Cities also make government assistance more accessible and can narrow some socioeconomic inequities. For example, while urban centers have higher rates of homelessness than rural areas, they also have more infrastructure to support homeless populations.

Cities are the future. If you can, choose to live in a city. If you already live in a city, advocate for some of the mechanisms discussed above. If you prefer to live outside of the urban core, consider tools like TDRs to protect your land from urban sprawl. We can all do something to propel our cities towards a more sustainable future.

Works Cited

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