Urban Flooding, Equity, and Green Infrastructure
Syracuse as Case Study
Urban flooding is an increasing challenge that cities face nationally and globally. Flood risk is often disproportionate, with some people facing greater risks and impacts than others. As cities invest in solutions to address urban flooding, will those investments help those most in need? How can race, income and other indicators of disproportionate impacts be taken into account in urban planning in order to make flood mitigation policies and practices more equitable and just?
This story map focuses on Syracuse, NY. We explore the ambitious green infrastructure program that Onondaga County has successfully implemented targeting the city’s water quality problems related to the Combined Sewer Overflows (CSO) caused by its Combined Sewer System. We also discuss shortcomings of these efforts related to concerns about inclusion of flood risk reduction and need for more explicit environmental justice (EJ) considerations. By incorporating EJ dimensions more explicitly, the county and the city could further strengthen their green infrastructure initiative, providing protection from flooding to its most vulnerable communities. Based on our research, we propose a methodology that American cities could apply to both incorporate flood risk mitigation in their planning, as well as to prioritize intervening in locations that could benefit vulnerable communities.
Green infrastructure (GI) has emerged as a powerful tool to mitigate the risks posed by stormwater in a decentralized manner. There are many ways to plan, design, and even define green infrastructure. While it can be used to deliver a wide variety of benefits, such as providing shade on hot days, or green spaces for communities to recreate, green infrastructure is most commonly defined as a tool for stormwater management, slowing down stormwater so that load on sewer systems is reduced. GI has potential to both mitigate flood risk and reduce combined sewer overflows. However, the latter use is usually given much more importance, driving how green infrastructure is designed and in what parts of the city it will be prioritized.
Funded by the Kresge Foundation, the Environmental Justice of Urban Flood Risk and Green Infrastructure Solutions project co-led by the Urban Systems Lab aims to better understand distributional environmental justice considerations related to climate change risks and urban flooding in vulnerable communities across the U.S.
Case Study: Syracuse
Onondaga County
Syracuse is located in Onondaga County, New York along the shore of Onondaga Lake.
The City of Syracuse
With 142,749 inhabitants, it is the 5th most populated city in the state. It has 51,925 buildings, and 468.5 miles of roads.
A City That Sits in a Valley: Flood Risk
Syracuse faces important challenges due to its proximity to water bodies, its topography, and the accumulation of impervious surfaces due to urbanization.
First, flash flooding is a recurrent problem because the city lies within a valley that feeds runoff to Onondaga Creek and Harbor Brook, often causing damage to homes and infrastructure, and the loss of human life. The impact of flooding in Syracuse may be disproportionate on certain communities. As part of our work, a parallel study observed that the areas which experience the most flooding are also inhabited by more vulnerable populations, as well as communities of color (1).
A City That Sits in a Valley: Combined Sewer Overflows
Second, the center of the city has a combined sewer that discharges into Onondaga Creek and Harbor Brook. Until recently, Syracuse’s CSO discharges were an important problem for the water quality of Lake Onondaga. However, the implementation of green infrastructure has improved the water quality of the lake considerably (2).
Race, Poverty & Flood Risk
A Redlined City
Understanding the distributional injustice of flood risk in Syracuse requires a look into the past. Syracuse is one of the cities that was assessed by the Home Owners’ Loan Corporation (HOLC - a federally backed corporation) during the 1930s and 1940s. The goal of this assessment was to map the financial security of providing mortgages in several American cities. Neighborhoods were graded in four categories (A, B, C and D), where A implied a minimal risk for investors and D, colored red, implied a “Hazardous” risk. Loaners were recommended to refuse providing mortgages in these redlined neighborhoods.
Race, ethnicity, and class played a key role in the classifications made by HOLC. “Green” neighborhoods rated with an A were inhabited by white and wealthy residents, while redlined neighborhoods were predominantly African American and European immigrant communities.
The process of redlining had dire consequences. While people living in neighborhoods graded D were unable to access loans and homeownership, capital and investment was directed towards wealthier, white areas.
Click here for an interactive map of Syracuse's redlined neighborhoods:
A Legacy of Segregation
Although currently not in practice and illegal, the legacy of segregating policies like redlining is still visible today. Most communities that are predominantly Black or African American are located in areas of the city that were graded with a C or a D.
Click here for a report on the current segregation in redlined US cities:
Correlation Between Poverty and Race in Syracuse
Race and Poverty
In addition, poverty and race overlap across Syracuse. Areas with a higher poverty rate tend to overlap with higher proportions of BIPOC residents. In 2010, Syracuse was ranked the 9th most segregated city in the U.S. Given the disproportionate distribution of flood risk and the legacy of segregation in the city, ensuring that climate adaptation measures benefit those most in need is crucial.
Segregation and Flood Risk
Predominantly Black communities in Syracuse, which overlap with formerly redlined neighborhoods, are also located in the lowest lying areas of the city, by the Onondaga Creek. Looking at these two maps, the link between legacies of segregation and current flood risk is clear.
Green Infrastructure
Adapting to water: Syracuse’s successful GI initiative
Since 2009, the County has installed hundreds of green infrastructure interventions to address the city’s water quality challenges through a program called the Save The Rain Program (2). Focused on mitigating the impact of the city’s Combined Sewer System on aquatic ecosystems like Lake Onondaga, green infrastructure has been consistently placed in locations within its CSO area.
The Save The Rain Program reached the goals set for reducing CSOs sooner than planned, becoming an example of successful GI implementation for improving water quality.
Green infrastructure in Syracuse - Who benefits today?
However, prioritizing green infrastructure for mitigating CSOs did not account for the distribution of benefits -- such as mitigating heat, providing green public space, or reducing flood risk -- to socially vulnerable communities. While the location of most of the GI interventions overlaps with vulnerable communities at the census block group level, a closer look reveals that many interventions are located on blocks with very low or no population at all, providing no flood risk protection to homes.
Zoom in and use the slider to explore overlap between green infrastructure, poverty and uninhabited areas.
Green Infrastructure located downstream from areas that might benefit from its flood risk protection
What about flood risk?
Several green infrastructure interventions are located downstream of residential areas, providing homes no protection from flooding.
This case raises a question: How could future GI initiatives be strengthened by incorporating flood risk and social vulnerability into the planning process? A funding program in the city, the Green Improvement Fund (GIF) , is providing economic support to GI projects in specific CSO catchments in the city of Syracuse. Increasing the annual capture capacity of the city to reduce CSOs remains the primary goal, as well as the main criteria to determine funding eligibility for proposed interventions.
In the following section, we present a methodology that allows cities to account for the social vulnerability of residents and households, and to use that information to prioritize spatially where to invest in GI to benefit those most in need.
Our Methodology
Incorporating flood risk and social vulnerability
Using modeling and mapping tools, we have adapted a methodology (3) that leverages flood risk mitigation and social vulnerability in GI planning. This methodology has been tested in two Syracuse sewersheds:
- Sewershed 039 is one of the sewersheds prioritized by the GIF for investing in GI. This sewershed is divided by Interstate 81. On the West of the Interstate, the sewershed includes some residential areas, while the Eastern side mostly overlaps with Syracuse’s campus and a large cemetery. We chose this sewershed to provide an example of how our method could inform the Green Improvement Fund.
- Sewershed EBSS is a larger sewershed with a larger population and highly vulnerable communities, in addition to having an industrial and logistical area to the North that is connected to Interstate 690. In addition, this sewershed has experienced flooding in the past. The combination of different land uses makes it a great case study to reflect on what to prioritize.
By incorporating flood risk and social vulnerability as critical EJ variables in green infrastructure planning, we aim to expand who may benefit from green infrastructure, and how.
This approach builds upon the work published previously in Vercruysse et al. (2019), a study in which a team of researchers mapped the impact of removing precipitation in different parts of a study area.
Preparing for a Baseline Simulation
The methodology begins with a baseline simulation (4) in the sewershed. As a baseline, we run a given storm across the entire sewershed (e.g. a 1 hour, 10 year storm).
To simulate flooding in the model, we add the layers that our modeling approach considers, such as green areas that infiltrate water….
… and buildings, that act as blockades against surface runoff, rerouting its flow.
Visualizing Flooding
After simulating the baseline storm, we can visualize the areas in the sewershed that experience different degrees of flooding.
Preparing GI scenarios and Simulating the impact of hypothetical GI
We then break our study area into smaller, equally sized sections or sub-areas (250x250 meters).
Changes in flood risk in each scenario
After running all the scenarios, we compare the baseline results to each of them. We can then identify the areas that show lower flood depths thanks to capturing the first inch. With this information, we can map the area that benefits from each scenario by experiencing lower flooding.
Below we show some examples of the lower flood depths that result from capturing precipitation in the three highlighted cells in the map. For example, the dark grey areas shown in this map represent the parts of the sewershed that experience lower flooding when the highlighted area captures the first inch of precipitation in a 10 years storm...
...And this is the area that benefits from capturing precipitation in the South East highlighted section. Because this sub-area his a steep slope, there is a wide area that benefits from the capture since less runoff is flowing down the hill.
And this is the area that benefits from capturing rainfall in the north of the sewershed. In this example, most of the flood depth mitigation takes place on the roads.
Tracing beneficiaries in each scenario
Now that we know the areas that experience lower flood depths thanks to capturing the first inch of rain in each scenario, we can overlap its contour with other socioeconomic datasets to assess the characteristics of the communities and built environment that benefits from reduced flood risk.
For example, we can collect information on the total residential area that benefits from each scenario. According to this criteria, one of the three scenarios shown does not affect any residential parcel at all.
We can also analyze the racial composition of the census blocks that benefit from each scenario. For example, which scenario better benefits communities of color?
Toward Equitable GI Planning
Making Sense of the Data
By overlapping the areas benefited in each scenario with a set of socioeconomic indicators, we can explore how the benefits of capturing precipitation in different parts of the sewershed are distributed differently across communities and infrastructure. Where would we place green infrastructure if we wanted to prioritize mitigating flood risk on roads? Would we place it in the same locations if we aimed to benefit residents experiencing poverty?
Click on the buttons below to see how different prioritization criteria highlights different areas of the sewershed. You can also click on the different areas to obtain the indicator used and its value in different locations of the sewersheds.
Conclusion
Syracuse is far from the only American city facing a long history of systematic disinvestment in BIPOC communities. As American cities plan, propose and implement GI interventions, the legacy of racist policy and its lasting environmental justice implications must be taken into account to allow for a more critical approach in developing solutions to climate risk in cities. Cities must employ a nuanced and comprehensive approach to GI planning that actively challenges the impact of this legacy by making environmental justice the priority. In order to achieve more equitable and just climate adaptation, cities need to incorporate social vulnerability and race both into baseline assessments and the planning of interventions.
The methodology we have proposed affords the flexibility to incorporate and prioritize multiple variables into GI planning, not only in Syracuse but in other cities as well. By accounting for and integrating the social and economic complexity of EJ considerations into the standard GI planning framework, cities can move towards a more just and equitable model.
Would you like to learn more about our work on urban flooding, climate change, and environmental justice? Do you find this approach useful for your city’s upcoming green infrastructure plan? Do you have thoughts and/or feedback on this story map or your experience as a reader? We would love to hear from you! Feel free to visit the project website and contact us at urbansystemslab@newschool.edu or herrerop@newschool.edu .
Footnotes:
(1) For more information on the baseline assessments in our case study cities, visit the project site (http://urbansystemslab.com/urbanfloodrisk).
(2) Information on the Save the Rain Program, through which the city of Syracuse has developed hundreds of green infrastructure projects to tackle the city’s CSOs, can be found in the Program’s website (https://savetherain.us/). For information about the impact of the program on the water quality in Lake Onondaga, you may visit https://savetherain.us/onondaga-lake/.
(3) This story map briefly presents our methods and tools, but we are unable to present the whole sweep of assumptions and details involved. If you are interested in learning more, you may visit the project’s website (http://urbansystemslab.com/urbanfloodrisk) or reach out to us.
(4) To simulate flooding due to a given storm, we use CityCAT, a hydrodynamic modeling tool developed by researchers at Newcastle University (UK) that is specially useful to map flood risk in urban environments. Researchers V. Glenis and S. Birkinshaw provided the model and guidance to use it. To learn more about the model, you may visit the project’s website ( http://urbansystemslab.com/urbanfloodrisk ) or this peer-reviewed article that presents the model.
The development of this story map benefited from the information, data and feedback provided by Adam Woodburn (Onondaga County), Zachary Monge (Jacobs), Khris Dodsdon and Cliff Davidson (Syracuse University).
This story map was developed by Pablo Herreros Cantis, Chella Strong, Claudia Tomateo, Chris Kennedy, and Timon McPhearson. USL Research Fellow Pablo Herreros Cantis and Director Timon McPhearson co-lead the project “the Environmental Justice of Urban Flood Risk and Green Infrastructure Solutions'' with support from the Kresge Crews Program, and in collaboration with Groundworks Hudson Valley.
