The Evolution of Cities: How Ecology Holds The Key To Our Infrastructure’s Future
by Igor Bronz, Phoebe Mankiewicz, Dr. Paul Mankiewicz, Joshua Harrison, Michael Fishman
The efficacy of urban ecological infrastructure is largely governed by something far simpler than many would believe — the amount of vegetation covering a given surface area. There are several nuances to this, but the general rule holds true — the more plants you have layered over a landscape, the better your environment is going to be. The key is finding enough surface area within our existing built environment to cover with appropriately designed layers of dense vegetation.
Green cities typically conjure a neo-Corbusian vision of gleaming renderings, — ultra-LEED certified, futuristic steel-and-glass buildings, laden with solar panels,- the latest technology. This mirage promises zero emissions and campuses populated with manicured green lawn punctuated occasionally with trees. Alternatively, albeit less commonly, our future is sketched as a series of green ziggurats, buildings staggering under loads of plants with but little resemblance to the urban landscapes we know. Neither vision incorporates traditional, working streetscapes at human scale. Both visions point to a reliance on high tech solutions in a society that has transcended traditional ideas of industry, supply chains, waste, and ecology. Nature looks upon these utopian landscapes with kindness, deciding to suspend the laws of biophysics in their favor in the first case, or economic realities in the latter. Futuristic visions of newly constructed ecological societies do not account for the reality of our built environments. Nature is not easily swayed by marketing pitches, instead, it is ruled only by the cold but quantifiable realities of surface area, fluid dynamics, boundary layers, and biological processes.
New York is no longer the most populous city in the world, and nowhere near the largest by land area; however, it is third in the world by number of skyscrapers, behind Hong Kong and Shenzhen. As such, New York is a tall city, and with great height comes great surface area. Its 321 square mile footprint¹ contains roughly 62 square miles of rooftops², over 192 square miles of vertical surfaces³, over 121 square miles of street surfaces⁴, 0.45 square miles of vacant indoor space⁵, and several cubic miles of under-utilized space below ground. From the perspective of the planet’s biosphere, this built environment is a virtual blank canvas waiting for innovative ways to bring its forms and surfaces to life, representing over 315 square miles of “land” area, along with a 520-linear mile coastline ready to invest natural resources such as sunlight, rainwater, and daily tides into habitats that house the return of land plants, saltmarsh, mussel bed, and oyster reef. Yet we continue to squander the opportunities these resources represent through our own inattention.
To address the numerous environmental impacts that come from supporting the billions of individual and collective actions that embody a city like New York, we can begin by viewing existing cities as substrates for living processes, and human activity as just one part of the larger system. As a start, vegetation could be integrated across every surface that could reasonably support life. Bare underpasses, covered in vegetation, could trap multiple tons of air pollution each year⁶ (seen in Figure 3) while utilizing the billions of gallons of runoff that overwhelm the NYC sewage system every year⁷ as a resource rather than allowing it to pollute our waterways.
The Urban Heat Island Effect, a phenomenon that results in higher temperatures in cities compared to nearby suburban or rural areas, is a product of the way we build cities, and is responsible for the premature deaths of millions in urban centers worldwide, however this global phenomenon could be reversed by integrating layers of dense vegetation into our city rooftops, walls and streetscapes. How effective is vegetation at cooling the air? Imagine you have plantings running along a sidewalk that are 5 feet wide. A ¼ inch of rainfall on these plantings would allow them to generate enough cool air through evapotranspiration to cool the sidewalk by 10° F. Basically turning a 90° F degree experience into an 80° F degree experience for the immediate area. A heavier rainstorm would get taken up by the soil underneath these plantings and provide days of cooling. Now imagine this vegetation was everywhere around you. Properly scaled, this daily work of vegetation can eliminate the Urban Heat Island. Widespread use of concrete or asphalt in urban construction has contributed significantly to this pattern, but their thermal impact could be mitigated with vegetation cover as well. Without multiple layers of leaves and the water that powers them, rainforests would be just as uninhabitable as deserts, or the bare concrete and brick surfaces of our cities. In utilizing vegetated roofs, walls and streetscapes at the right scale, we stand a chance at not just reducing environmental issues but reversing them. By utilizing the capacity of vegetation to fight one major urban environmental issue (Urban Heat Island) and powering it with the output of another ecological problem (billions of gallons of stormwater runoff), we are creating an ideal solution. Reintegrating ecological function into barren built environments give us a chance to turn depreciating, energy-intensive landscapes into appreciating assets: biologically productive systems capable of transforming local environments, impacting not only temperature, but water, food and waste as well.
“…but as far as the environment is concerned, technology is not a replacement for ecology.”
What will this regenerative New York City actually look like? Most likely, nothing like the sterile renderings we often see. A resilient New York City could include towering vine covered walls, vegetated bike lanes, wetlands separating road from sidewalk and pedestrian, parks that double as sponges to absorb rainfall, and rooftop bars that resemble your favorite hiking vistas. Rather than excluding nature from our lives, we can embrace the complexity and utility of plant cover as the medium of choice for city surfaces.
In the arena of urban green infrastructure, there is a trend in focusing urban carbon neutral or even carbon negative strategies in cities on entirely new construction. This suggests that what we already have is somehow technologically insufficient at its core. There is some truth to this — old buildings, on average, tend to be less energy efficient than new, purpose-built LEED structures — but as far as the environment is concerned, technology is not a replacement for ecology.
The Bank of America Tower in Manhattan is a good example. Its 55-story crystalline structure is composed of low-emissions concrete and energy-efficient window glazing, not to mention the dozens of other ‘smart’ features intended to recycle various outputs and collect data⁸. This tower is the first Platinum LEED-certified skyscraper in the world and was intended to be the gold standard of sustainable skyscraper design, yet according to data released by New York City in 2012, the Bank of America Tower produces more greenhouse gases and uses more energy per square foot than any comparably sized office building in Manhattan⁹. Opponents of these claims argue that this tower employs technology to reduce stress on existing electrical infrastructure and offset its carbon footprint in other ways. There is considerable debate over the total environmental impact of the Bank of America Tower, however 2019 regulations on greenhouse gas emissions would nevertheless result in this structure facing heavy fines. While it checks the boxes on its LEED rubric and takes genuinely effective steps to advance sustainability in skyscraper construction, it also leaves much to be desired in quantifiable ecological performance. Perhaps in spite of its technological advancements, the Bank of America Tower raises an important question: just how green can an all-glass building possibly get? Simply by gazing at the façade of the Bank of America Tower, one notices that there is not a single leaf to be found.
From a financial perspective, rebuilding is much more costly than utilizing existing tools and materials to retrofit our existing infrastructure. If planned carefully, retrofitting our city could cost a fraction of the fortune required to replace existing buildings and bridges and doesn’t require displacing the millions of people living and working here. We don’t need to rely on visionary technology or spend tens of billions of dollars towards ever increasing efficiency barriers; Instead we can acknowledge the power of billion-year-old technologies that turn sunlight, water and CO2 into oxygen and sugar.
Although the COVID-19 pandemic temporarily halted construction, New York City typically produces ~16,500 tons of C&D waste each day on average¹⁰. That translates into 33,000,000 pounds of concrete, soil, stone, brick, asphalt and glass waste, every single day. As C&D waste accumulates at construction sites, over 1,000 private companies operating in NYC truck this material to the more than 40 waste processing facilities in and around the city. 60–100% of this waste constitutes fill materials (stones, concrete & earth) and are recycled, however only about 40% of non-fill materials (everything else) are recycled¹⁰. This remainder gets trucked to landfills, usually out-of-state, at great expense both to the producer and to the environment.
In order for NYC to “go green”, this immense volume of waste-stream material must be integrated or recycled in some way in order to decrease our carbon footprint. One option is to use this material locally to construct soil substrates for plant growth, to provide the basis for marshes, mussel beds and oyster reefs on our coastlines, and create aquifers underneath streets to take up stormwater and utilize it to power plant growth on walls and roofs.
Plant growth would cool our city and insulate our buildings through the process of evapotranspiration, all while using stormwater that our wastewater treatment facilities would otherwise process at significant cost, and creating biodiversity corridors currently absent from NYC. From a health and social perspective, these initiatives could save lives by reducing air pollution and heat loads, create local jobs reducing poverty and crime, create opportunities to grow fresh vegetables and herbs in food deserts, and give residents a sense of participation and ownership of their communities.
According to our own carbon capture model (adapted from the EPA’s Greenhouse Gas Equivalencies Calculator), covering roughly 25% of NYC surfaces (roofs, walls, streets, coastlines and offices) that already exists with vegetation would remove over 6 million tons of carbon from NYC’s 52 million ton annual carbon budget, without requiring new multi-billion-dollar structures or investing in costly, unproven sequestration technologies. Solving environmental issues doesn’t have to require software or incremental increases in efficiency, it can be done with vegetative hardware. More importantly, solving environmental issues can be done with vegetative hardware grown upon urban water and waste cycles and utilized at a scale that makes a difference.
At the current carbon price of $50/ton¹¹, 6 million tons of carbon saved would be worth roughly $300 million/year. But it’s not just the carbon: this equates to over $600 million in annual savings¹² on electricity, roughly ⅔ of which¹³ would benefit residents directly, over $1 billion in annual savings on wastewater treatment¹⁴, in addition to potentially billions annually in other systemwide savings such as waste recycling, taxable income from new jobs, lower social services reliance, better health & wellness outcomes across the board, and increased marketability of newly created public spaces. The cost of adding this much green surface cover to existing structures would be between $50–100 billion¹⁵, and require minimal maintenance. Based on this cost, the payback period would be less than 40 years; after that the savings accrue indefinitely. Investment in effective ecological infrastructure is an appreciating asset, so as the system matures, it becomes increasingly self-sustaining and more effective from an ecological standpoint.
We at Leaf Island take sustainable city design within the context of urban health, finance, and social justice seriously, therefore we do not rely on the promises of technological ‘silver bullets’, but rather on billion-year old technology that has supported human life on earth so far. Integrating vegetation with as many city surfaces as possible and ensuring this vegetation has access to water and sunlight allows nature to do the rest. Nature does not recognize waste nor does it require profit to function, unless you count biomass, where every output is another input. Above all, nature works for free.
Sources:
- NYC Dept. of City Planning-Land Use Facts, 2002
- https://www.urbangreencouncil.org/sites/default/files/sustainable_roof_laws_brief_final_12.11.19.pdf
- PLUTO 20v8 Database
- Estimated using average combined street and sidewalk width in NYC (80 ft) by number of miles of streets & roads (~8,000 miles, from: https://www.cityandstateny.com/articles/politics/new-york-city/how-nyc-will-close-100-miles-streets-cars.html)
- https://qz.com/1953045/vacant-new-york-office-space-for-sublet-is-up-91-percent-since-2019/
- Adapted from findings in https://www.fs.fed.us/nrs/pubs/jrnl/2014/nrs_2014_nowak_001.pdf
- https://www1.nyc.gov/assets/dep/downloads/pdf/water/stormwater/stormwater-design-construction-guidelines-2012-final.pdf
- http://www.greeneducationfoundation.org/green-building-program-sub/case-studies/892-bank-of-america-tower.html
- Sam Roudman https://newrepublic.com/article/113942/bank-america-tower-and-leed-ratings-racket
- http://journeys.gettingtozero.nyc/construction-and-demolition#:~:text=Currently%2C%20New%20York%20City%20has,%2C%20NYC%20DDC%2C%20May%202003.
- https://www.edf.org/true-cost-carbon-pollution#:~:text=The%20social%20cost%20of%20carbon%20is%20a%20measure%20of%20the,per%20ton%20in%20today's%20dollars.
- According to our internal carbon capture model, 2.85 billion kwh saved at a cost of $0.21/kwh, between heating and cooling cost decreases and wastewater treatment.
- https://www.ny-engineers.com/blog/how-does-nyc-use-energy
- Cost of wastewater treatment is $6.2/100 cubic feet (https://www1.nyc.gov/assets/nycwaterboard/downloads/pdf/blue_book/nyc-rate-report-fy20.pdf) — volume adapted from internal climate change model
- 22.3 billion square feet of NYC surfaces (~25% of NYC) can be retrofitted at a average cost of $3–4/SF using well-scaled construction practices
