• Mark Reiner, PhD, PE

Urban Ag, Green Infrastructure, and Long-Term Carbon Sequestration

Updated: Mar 3

Is urban agriculture considered to be “green infrastructure”? Are large commercial vertical farming ventures considered as urban agriculture? This blog series initiates a discussion to define these questions to better deliver urban climate action initiatives.


On January 29th, 2020, an article entitled “House Democrats Release $760 Billion Green Infrastructure Plan” was emailed to me by one of the other authors of this blog series. My initial thought was that this is an inordinate amount of money for such a specific infrastructure sector – Green Infrastructure (GI). However, after a quick glance, it was obvious that the bill covered all infrastructure sectors and the term “green” was used because “…additional funding [was added] to address climate change across these areas.” Are we using the term “green” in infrastructure policy to go beyond even greenwashing, but using it to imply adaptive infrastructure resilience to the impacts of climate change and mitigative properties to reduce anthropogenic carbon emissions? In short, does it matter how we use the term “green” when developing urban climate action infrastructure initiatives?


In order to address these questions, this blog series begins by examining the relationships between urban agriculture (ag), GI, and commercial vertical farming enterprises. Then we expand the discussion to a regional perspective to identify opportunities for long-lasting carbon sequestration to achieve real climate benefits. This broad view is provided by different authors in this series. Each with the commonality that better understanding how we use the term “green” will lead to more solid urban climate action policies. The series concludes with an overview of the existing systems and opportunities for urban ag flourishing in Denver, Colorado.


Connecting Green Infrastructure to Food and Climate Action

Common definitions of GI do not include any climate benefits, but instead are centered around the more terrestrial-bound environmental benefits of natural stormwater attenuation and treatment. The EPA uses Section 502 of the Clean Water Act to define GI as "...the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters." The tendency to focus on the words “…plant or soil systems” leads to assumptions that “green” provides climate benefits - without any required methodology. But, an even more narrow view of GI is given by the National Green Infrastructure Certification Program (NGICP) that defines GI as: “Stormwater management practices that protect, restore, or mimic the natural water cycle…”. Where “mimic” can essentially remove any natural components to the project. However, as cities are required to meet EPA stormwater regulations, as opposed to voluntary carbon mitigation actions, these GI projects are very popular – but provide no mandatory climate benefits. The point being that without requiring a methodology for quantifying carbon mitigation of GI projects, this remains a key challenge for integrating GI into climate actions (as posed in Linda Romanovska’s comprehensive paper , specifically, Challenge 5). The intent of this blog series is not to minimize the positive stormwater impacts, but focus on the climate change mitigation assumptions associated with GI and urban ag.


Figure 1 presents a challenge for differing between public urban ag, GI, and indoor commercial vertical farming. Consider the three juxtaposed photos of an open urban garden and a container farm (CF). The picture on the left (a) is a typical urban garden. The two other images are vertical farming from the inside of a CF (b), and the outside of a CF (c). According to the EPA and NGICP definitions of GI, only the outdoor ag (a) would be considered as GI. But, during two separate tours of a CF during the summer 2019, I asked each group whether they considered the vertical farming inside the CF (b) as GI? They responded that it was – for sure. But, when the same groups were asked if the outside of a CF (c) was GI, they responded that it was not – at least from what the community could see of the project – just another ugly intermodal shipping container in the urban built environment. No connection to the soil or drainage.

Figure 1: a) open plot urban ag b) vertical farming in a CF c) exterior of a CF

However, consider how the potential yields of produce that greatly differ the open plot urban ag (a) to the CF (b). Although there are no standard plot sizes for urban gardens, a typical size may be about 20’ x 20’ (400sf). In addition, the growing season is not year-round in the open plot (at least in Denver). In comparison, the footprint of a CF is also 400sf, but has a 24/7/365 growing season and grows vertically. Using lettuce as an example crop, each CF can grow as much as 49,000 plants per year – a yield equivalent to about 2 acres of farmland (>87,000sf, over 200 times more produce per unit area), while using at least 95 percent less water. The vast differences in outcomes between open plot and a CF (e.g. aesthetics and community well-being of the open plot vs entrepreneur maximizing yields for specific markets) seem to warrant new classifications in urban ag differentiating public from enterprise.


And yet, all three images in Figure 1 have a commonality in that they do not actually contribute significantly to carbon mitigation. The energy used in a CF (assuming grid) is likely (this blog is just posing questions) offset by the reduced transportation of farm-to-fork. And for the open plot, unless strict regenerative practices are used, the topsoil carbon oxidizes back into CO2 whenever turned over. Whereas vertical farming generally has no soil at all due to hydroponic or aeroponic practices. And, for both the open plot and vertical farming, although plants absorb carbon while growing using photosynthesis, they also respire the same amount of carbon when consumed. A life-cycle of only a few months.


But it is the much higher yields of produce and vastly reduced water consumption of vertical farming that sets up a broader urban-rural and climate action discussion. How should cities view water, carbon, and the importance of a positive urban-rural relationship as they relate to effective urban infrastructure resilience climate action policies? Perhaps the adage should be that we ‘live locally, act regionally, and think globally’ to achieve a McDonough defined carbon positive approach.


Reframing the Urban-Rural Water Conflict to a Carbon Harmony

There exists an urban-rural conflict over water that is ubiquitous wherever there are fast growing municipalities surrounded by rural areas that practice traditional farming in water scarce areas of the United States. Given the status quo of water planning for population growth, and that water is an unpredictable finite resource subject to wide variations in natural supply, the conflict will continue to exacerbate and change is inevitable. As Ralph Waldo Emerson stated: “Cause and effect are two sides of one fact.”

Using Colorado as an example, consider a high-level view of how water is consumed. Approximately 60 percent of the of water that originates across the state each year (average of 13.7 million acre-feet), exits the state for downstream users. Of the remaining 40 percent (average 5.3 million acre-feet) of the water that is consumed in Colorado, approximately 89 percent is committed for agricultural purposes (70 percent of freshwater withdrawals, globally) across 2.6 million irrigated acres and 10.6 million acres of cropland. Yet, over 86 percent of Colorado’s population live in urban areas and consume just 7 percent of the water. As municipalities in Colorado plan for continued population growth, water demand will increase nearly a 20 percent. Similarly, the agricultural demand for water will also increase due to the increased need for food and the impacts of climate change The conflict is current and the rural-urban relationship is already under considerable strain as evident in a fairly recent Denver Post headline that read: “Colorado Divide: Seismic shifts create rural-urban chasm in the culture, economy and politics of the state” (Denver Post, Jan. 24, 2018).


Yet, water conservation from urban areas alone will not be enough to meet increasing demand, especially when considering that the growing urban population will simultaneously demand more food productivity from rural communities. When there is conflict over the supply of such an important resource, it may be a natural impulse for urban residents to call on rural communities to reduce consumption, either proactively with drip-irrigation, or punitively by changing diets due to facts such as that each pound of beef requires 1,847 gal water. Either way, an antagonistic rural-urban relationship exists and requires a solution. After all, no city can be considered as sustainable or resilient without fully embracing the fact that nearly 100 percent of all food, fuel, water, and materials originate as natural resources in rural areas (aka, hinterland) and transported into the city. The rural-urban relationship must be symbiotic in order to thrive.


Perhaps resolution to this conflict could be framed by substituting carbon for water in the resource conversation. There is an equally polarized view of carbon as a resource between the rural and urban communities. While cities have “carbon war rooms”, the opposite is true for the rural communities that understand that carbon is the source of life. Indeed, all living things are carbon-based. My dog is carbon-based. This difference in the urban-rural perspective on carbon originates from not labeling carbon correctly. That is, it is not carbon that is a climate change driver, rather fugitive carbon in the form of carbon dioxide (CO2) emissions (carbon is 12 g/mol and carbon dioxide is 44 g/mol). Whereas the rural view is of pure carbon, or living carbon, the element that supports all life. What if urban climate action initiatives better linked the “war” to eliminate fugitive carbon dioxide with the rural demand for living carbon – permanently sequestered in soil?


Change is upon us. Now is the time to consider how we define GI and urban ag and integrate methodologies to address water consumption, and carbon sequestration in order to embrace “greenness”. And, while we’re at it, improve the resilience of the urban-rural relationships in urban climate action policies. These issues will be addressed in more detail in the subsequent parts to this series (all will be linked as they become posted).


Other (upcoming) Posts in this Series:

Critter Thompson: Describes how we define green infrastructure currently and why that's problematic and connects the Romanskva concepts to GI as it pertains to urban ag, water consumption, carbon mitigation, and resilience.

Andrew Fang: Describes what climate policy should look like based on the various urban infrastructure strategies we've thus far discussed - and what gaps exist in current policies that can be filled by this more holistic approach to GI.

Lisa Warren: Provides a comprehensive overview of urban ag potential for increased resilience and sustainability in Denver. Based on her proposal to Rockefeller that ties in actual players in this field.

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