Looking at Cooling Benefits of Plants Through NYC Vegetation Data
NYC neighborhoods are known to vary in local cuisine and culture, but a new analysis from the Just Nature NYC Partnership shows that in most neighborhoods, there is also a stark variation in how much vegetation there is, with clear implications for urban heat challenges — here we discuss what this means for New Yorkers, especially the city’s most heat-vulnerable residents.
Extreme heat is the leading cause of weather-related mortality in NYC, and urban vegetation can be part of the solution. A recent study led by researchers at the NYC Department of Health and Mental Hygiene looked at early morning air temperatures and found that plants can indeed have a local cooling effect in NYC, but only when there is “enough” local vegetation. At the center of an area about the size of seven baseball fields, air temperature started to drop when at least 32% of the area was covered in vegetation. In the highly variable landscape of NYC, neither people’s susceptibility to heat-related illness and death, nor vegetation cover is distributed evenly. What does this mean for residents? Is there enough vegetation to help keep residents cool in the most heat-vulnerable communities? As part of the Just Nature NYC Partnership, our teams at the New York City Environmental Justice Alliance and the NY Cities Program of The Nature Conservancy mapped local vegetation levels across the city to begin answering these questions.
The NYC Landscape
Some of the most recognizable physical characteristics of cities contribute to the urban heat island effect, or the tendency for cities to be warmer than nearby suburban and rural areas. The asphalt that absorbs and re-radiates heat, the limited green open space that naturally helps cool the air, and the millions of machines like vehicles and air conditioning units (ironically) which generate heat as they work — all warm the local climate. These environmental factors combined with socioeconomic characteristics ultimately factor into how susceptible people are to heat-related death, as reflected in the NYC Heat Vulnerability Index (HVI). Discriminatory policies, like redlining, have resulted in neighborhoods that are predominantly home to low income households and people of color bearing a disproportionate urban heat burden. These environmental justice communities often face exceedingly high exposure to warming features, like higher traffic densities, and have disproportionately low access to cooling features, like vegetation.
Plants, collectively referred to as “vegetation,” provide many benefits for biodiversity, people, and communities. Not least of which, plants can have cooling effects through shading and evapotranspiration — a welcome change as already sweltering NYC summers are getting even hotter with climate change. Plants — mainly trees, grasses, and shrubs — are found throughout NYC, including in forested natural areas and wetlands, landscaped parks and yards, and in more human-built features like rain gardens, green roofs, and street tree beds. Vegetation is a key part of supporting human health and wellbeing in a warming climate, especially in the most heat-vulnerable communities. However, for solutions to be most effective, their planning must account for local variability in the environmental conditions and socioeconomic characteristics that factor into heat vulnerability along with community needs and concerns.
Mapping Local Vegetation Across the City
Walking the streets of NYC, you can see that the amount and type of plant life varies from neighborhood to neighborhood, and even block to block. Lucky for us, walking was not needed for our mapping efforts because NYC land cover data, developed from high-resolution images of NYC and 3D information (lidar), are freely available in extremely fine detail of 6-inch by 6-inch squares. Plants are represented in this dataset as “tree canopy” and “grass/shrub” types of vegetation.
To carry out the analysis, we created a grid of points spaced 100 feet apart over the entire city and used the land cover data to calculate the percent of land covered by vegetation within a 200 meter radius around each point (Image 1). The citywide results are shown in the map below (Map 1) where the points have been converted to 100-foot by 100-foot grid cells. Areas in yellow have less than 32% vegetation (lighter shades indicate less vegetation) and areas in green have at least 32% vegetation (darker shades indicate more vegetation). The resulting data, shown in the maps below, are available for download in a long-term data repository, Zenodo, at https://doi.org/10.5281/zenodo.8370381.
Figure 1. Example point with a 200 meter radius circle around it, displayed over high-resolution aerial imagery from 2018, with the grass/shrub and tree canopy classes from the 2017 land cover dataset used in the analysis presented here. The point is just west of Green-Wood Cemetery, by P.S. 172. The aerial imagery and land cover data are courtesy of the City of New York.
Figure 2. Results of vegetation density analysis, zoomed to the entirety of New York City. Click here to view an interactive map.
We found that our initial questions were questions of scale and the answer to “Is there enough local vegetation to cool residents?” varies by borough, neighborhood, and even city-block. When zooming in on our results, some areas that initially appear heavily vegetated have pockets that are not, and vice versa. We can see these dynamics play out in two parts of the Bronx, as an example. Bronx Community District 8 (Map 2) ranks the fourth highest in vegetation cover across the city (almost 50% of the land area!) but there is substantial variation between some neighborhoods. Riverdale (towards the northwest) is heavily vegetated and with largely affluent and white residents has a low heat-vulnerability rating (HVI of 1 out of 5). Kingsbridge (towards the southeast) is sparsely vegetated, and with generally lower income households and a higher proportion of residents of color has a high heat-vulnerability rating (HVI of 4 out of 5). Using our localized approach we can identify areas like this, where there are opportunities to target greening efforts for the benefit of the neighborhoods most in need of cooling.
Figure 3. Results of vegetation density analysis, zoomed into Bronx Community District 8. Click here for the interactive map.
Figure 4. Results of vegetation density analysis, zoomed into Bronx Community District 2. Click here to view an interactive map.
Bronx Community District 2 (Map 3), which includes Hunts Point, has the third lowest percent vegetation cover (14% of the land area) of any district across NYC. Hunts Point is heavily developed, largely industrial and has a HVI rating of 5, but our analysis highlights local potential, with several spots approaching or above the 32% threshold (most notably coinciding with Hunts Point Riverside Park, Julio Carballo Fields/Manida Park, and Barretto Point Park). This insight could prove valuable in ongoing work in Hunts Point that envisions nature-based solutions, like vegetation, as a path toward climate resiliency.
One of the many useful approaches to improving community resilience is to increase community cohesion, which can be supported with greening. Increasing connectivity and resident access to clusters of vegetation by creating corridors of vegetation could be a useful first step in bringing an entire district above the cooling threshold. When communities have simple, established ways to allow residents to stay connected to their neighbors and protective resources (such as early warning systems and Be-A-Buddy programs), they have better odds of surviving disasters or emergencies, like extreme heat events. To determine the right steps to take, it is important to work directly and intentionally with the local community, uplifting them as the leaders of these processes. By centering their voices, we can learn what measures will be most useful to them, enabling their needs to be met and improving the conditions of the communities most at risk.
Local Context is Key
Building from our work, and in combination with a deep understanding of local context, there is an opportunity to channel available public funds to areas where even small increases in vegetation can lead to large positive impacts that benefit heat vulnerable communities. Considering the intersection of biophysical conditions and the many other factors that shape the local context (including the socioeconomic status of residents, city planning and political dimensions, and lived human experiences) will be crucial in using our analysis to catalyze successful on-the-ground solutions.
Adding vegetation without considering other aspects of the city landscape, especially the needs of the city’s heat-vulnerable residents, can have unintended consequences. For example, experiences in Harlem and Gowanus have shown that environmental justice gains can be co-opted by luxury developers and others who stand to gain from wealthier residents moving into a neighborhood at the cost of displacing members of low-income communities and communities of color. Ensuring residents are able to stay in their neighborhoods to feel the cooling benefits of vegetation can be achieved by pairing strategies to expand vegetation cover with proactive anti-displacement strategies. Such strategies may aim to preserve existing affordable housing, stabilize neighborhoods, or produce new affordable housing (along with market-rate housing).
On the flip side, including local residents — who know what the most important concerns for their neighborhood are — in planning from the beginning can create synergistic effects. Elevating local perspectives may help to select appropriate vegetation that ameliorates other community concerns such as food insecurity (e.g., food forests) and flood resiliency (e.g., rain gardens), while minimizing potential disservices of vegetation (e.g., allergies/pollen). Ultimately, the local context will determine to what extent the benefits of added vegetation reach heat-vulnerable New Yorkers and address their specific concerns.
What’s next?
This is our first blog post sharing the work Just Nature NYC is doing to advocate more green infrastructure, especially trees, across New York City to support climate justice and equity. Keep an eye out for an update on NYC-EJA’s CAMP-EJ report and extreme heat campaign, as well as further work building on this analysis. In the meantime feel free to explore the results in the interactive map, and download the output from the analysis to work with on your own — don’t hesitate to reach out with any thoughts or questions!
