The Urban Effect

When she was 12 years old, Karen Seto boarded a train traveling from Hong Kong to Guangzhou, roughly 90 miles, during a family trip to China. It was her first glimpse of the enormity of urbanization.

As the train pulled away from Hong Kong (“which is like New York City on steroids”), Seto was transfixed by fields of rice that seemed to go on forever, a verdant eternity that fed millions of people. But within minutes, those bucolic fields gave way to growing villages and tall buildings. Soon another city appeared: Guangzhou, which at the time was home to nearly 2 million but today, just four decades later, has a population of nearly 14 million people.

“That train ride had a really big impact on me,” Seto says. “I thought, ‘Oh, I’m leaving the city,’ but the city was never really that far behind — even in the countryside. It occurred to me that, from the urban to the rural, all of these systems — food, economy, transportation — were interconnected.”

Over the past couple of decades, Seto, Frederick C. Hixon Professor of Geography and Urbanization Science at the Yale School of the Environment (YSE), has become one of the world’s leading scholars on urbanization. Through pioneering work integrating satellite remote sensing imagery with socioeconomic data, she has helped advance scientific understanding of just how much humans are changing the face of the planet and what it means for the future.

At YSE, she is not alone in studying cities. Across the School, scholars and researchers are exploring the many dimensions of urbanization or working to create healthier urban systems. And beginning this fall, YSE will offer a new urban specialization to integrate the disparate but related challenges and fields of inquiry related to urbanization. The curriculum will include core courses in urban ecology and urbanization as well as a range of electives that draw on the wide array of experts and disciplines across YSE and Yale.

The fact is, there might not be any faculty member whose work doesn’t connect with urban issues in some way, says YSE Dean Indy Burke. “In the past, people didn’t really think of urbanization as an environmental focus of study — it was too local, relevant only in certain places, and detached from global concerns,” she says. “But over time it has become increasingly clear that the consequences of urban growth across the planet are linked to every environmental issue.”

In the new specialization, Burke says, students will examine how environmental change affects urban areas and how urban areas affect the environment, from local studies in New Haven to the region and the globe. But this isn’t just about identifying the challenges of urbanization; it will also explore the potential opportunities.

Shaping the cities of tomorrow

It is estimated that about 55 percent of the world’s population now lives in urban areas. By midcentury it will be more like 70 percent, including a surge in the number of megacities (those with populations of more than 10 million), largely in the developing world.

Researchers expect that this growth will intensify the burden on resources, consume vast areas of valuable agricultural land, and threaten biological diversity through habitat fragmentation in all corners of the planet. Increased demand for energy and loss of natural spaces will also likely exacerbate climate change.

Within the cities themselves there is an added risk; in many metropolitan areas, the urban heat island (UHI) effect, a common phenomenon that makes urban areas significantly warmer than surrounding areas, will only compound the consequences of climate change, increasing health risks for city dwellers.

Xuhui Lee, Sara Shallenberger Brown Professor of Meteorology at YSE, studies how the UHI effect and other factors are already changing life in the world’s cities — and what those changes will look like in the future. Sometimes that work is applied in a very practical way locally. Three years ago, he and Brad Gentry, Frederick K. Weyerhaeuser Professor in the Practice of Forest Resources Management and Policy at YSE, taught a capstone course that allowed students to evaluate the biophysical threats and social impacts of climate change in New Haven — and to make recommendations to city planners and administrators.

It can also be used to shape the cities of the future. In China, Lee’s insights have helped inform the design of Xiong’an, which will eventually be used as the country’s second capital. For the design, planners have tried to incorporate numerous sustainability strategies. Some are conventional: Many of the buildings will utilize the latest in green design. Others are more adventurous. During a recent trip, Lee was shown a system of riderless vehicles that transport food around the city’s streets. Consumers are able to stop the vehicles and, with the swipe of a card, purchase groceries before sending the vehicle back on its way.

Researchers from China have reached out to Lee as they plan the city’s layout, including the placement of streets and infrastructure. “They’ve asked me, ‘If you were to plan a city in such and such a way, would it create more of an urban heat island or less?’ If you’re careful, you can configure cities in a way that promotes the kinds of outcomes you want.”

Street-level insights

There is also an urgency to reconfigure the cities of today. As sea levels rise, many coastal cities can expect increased flooding, including when rivers and other inlets push more water farther inland during extraordinarily high tides and storm surges.

One of the ideas often considered to confront this threat is actually an old one: tide gates, which utilize flap valves that open and close to manage tidal flow, have been used for a variety of reasons for centuries. They are now being eyed as a climate mitigation strategy. In New Haven alone, tide gates have been used on two different rivers, the Mill and West rivers, for decades.

But the environmental results haven’t always been positive, says Gaboury Benoit, Grinstein Class of 1954 Professor of Environmental Chemistry at YSE and co-director of the Hixon Center for Urban Ecology. On the West River estuary, for instance, by automatically closing when the tide rolled in, the gates controlled flooding but altered the freshwater tidal system and degraded water quality.

“This design completely alters the upstream ecosystem and turns it into a fresh tidal system from a salt tidal system,” he said. “As you can imagine, whether you’re bathed in saltwater or freshwater, it is going to create a completely different ecosystem type.”

In a long-term study, Benoit is monitoring how a new, self-regulating tide gate system, funded by a local NGO, has improved saltwater flushing in the estuary and supported the recovery of plant and animal communities. “Because I have these very interesting local examples, it’s a New Haven-based research topic that has potentially global repercussions.” The project is one of many research areas that allow Benoit to examine the impact of human communities on water in greater New Haven. Benoit and his lab are also studying how litter and road salts affect water quality, the abundance of microplastics in the environment, and the potential benefits of other green infrastructure technologies.

For instance, working closely with the YSE-based Urban Resources Initiative, the city of New Haven, and several other partner groups, Benoit has helped install and monitor a network of bioswales — landscaped areas near roadways that capture and filter stormwater before it can reach the sewer system. The bioswales, which are in place throughout the city, reduce stormwater flooding, decrease contaminated discharge into the Long Island Sound, and have advanced the understanding of the benefits of this low-cost technology.

“I love that kind of work because it has an immediate positive effect,” he says. “It’s very applied, and the nice thing about it is that I think it makes people much more aware of the water cycle in cities.”

Equity and justice

Across the world, advances in technology and innovative policies are creating new opportunities for billions of city residents every year. But often those benefits don’t reach the world’s middle-income and poor people, says Narasimha Rao, an assistant professor of energy systems at YSE.

Rao, who came to Yale in 2019, studies the relationship between energy systems and human society. Perhaps nowhere are those links more complex than in the world’s urban areas. While millions of people stream into cities each year, he says, many are making that decision for the wrong reasons. They’re not lured by the promise of new opportunities but are forced to move because of lost jobs or livelihoods.

And when they arrive, they encounter a host of risks, from the high cost of living to elevated health threats. Using a combination of qualitative and quantitative research, Rao is examining why it is that so many people struggle to achieve well-being — including access to healthy foods and affordable air-conditioning — despite being surrounded by vast wealth.

In India, for instance, he has found that urban populations have access to a less nutritious and diverse diet than rural ones, despite the seemingly endless food offerings found in cities. Why? Because access to many food options are too expensive or simply unavailable to poor communities.

“The challenge is that you often find greater inequality in cities compared with rural areas,” he says. “Yes, there are higher concentrations of wealth, but you also have stark poverty, so often these innovative developments aren’t available to a broad population.”

Looking to the city

As a student, Karen Seto never intended to specialize in urbanization science. As a matter of fact, she never even took a class on urbanization. Her interest in the subject emerged from her interest in land system science. In time she came to see that you simply can’t separate land use from urban growth.

During the early 1990s at Boston University, she became part of a group of scholars that, long before Google Earth or the availability of data from commercial satellites, was taking advantage of NASA satellite data and advances in remote sensing to monitor, characterize, and map global land use.

“It was incredibly novel back then,” she says. “We were on the forefront of using these data and integrating them with other types of data and analysis. The bird’s-eye perspective and regular observations of the planet available through satellite data enabled us to see things that the naked eye couldn’t see.”

Over the years she has explored how urban growth is exerting pressure on biological diversity, food systems, and the climate (including as one of two coordinating lead authors of the urban mitigation chapter in the UN Intergovernmental Panel on Climate Change’s critical climate reports). But this work has also revealed promising insights into the relationship between urban form and environmental impact.

And it has put a spotlight on numerous cities that have become models for sustainable design and green policies. From Taipei (which has invested in green energy, public transportation, and sustainable waste management) to Minneapolis (which has prioritized transit-oriented development), a growing number of cities have embraced sustainable practices and seen reductions in carbon emissions.

“Most of the world’s population will live in urban places in the decades ahead, so that’s where the demand for energy, for food, for resources will be greatest,” she says. “But cities are also the places where so many sectors come together — and where you’re more likely to get things done. It can be difficult to roll out a strategy on a national scale, but if you can test solutions in a few cities and show that they work, then it’s easier to adopt them at a larger scale. That’s pretty exciting.”