Norfolk, Heat Islands, and the Urban Canopy

by | Nov 22, 2021


State Senate Bill 1393 is up for renewal during the 2022 General Assembly. It expands localities’ authority to exceed the minimum requirements in their tree replacement and conservation ordinances — a rule that state law currently limits. Under specific development circumstances, such as stormwater permit requirements, areas of recurrent flooding, formerly redlined areas, and comprehensive plan compliance, localities would be able to require more than the legal minimums for tree protection and replacement. This bill also authorizes the establishment of a stakeholder group to develop and recommend policies for tree conservation and proliferation to state and local governments. The Chesapeake Bay Foundation supports SB1393; you can read more about it here. This series of articles explains why urban tree canopy is so beneficial to air quality and inspires readers to contact their local representatives to support this bill. 


Urban tree canopy is the layer of leaves, branches, and stems covering the ground when viewed above. It’s the leafy green umbrella that protects us city-dwellers from the blazing summer sun and seasonal downpours. Meander through Ghent in the summer and admire the delicate crepe myrtle blossoms while feeling a cool mist as you pass beneath them. Shelter under the branches as you try to stay dry in a sudden rainstorm. Sigh with relief as you finally reach a patch of shade on your 2 pm walk to 7-11. Witness the eternal struggle between squirrel and dog, as the former taunts the latter from the safety of a 20-foot vertical. Watch the leaves change in the fall and crunch through them as they collect on the sidewalk. The urban tree canopy is pretty rad and provides us with many economic and health benefits through the ecosystem services of trees. But will these services continue? And do they benefit all of us equally? 


Traversing Norfolk (or any urban center) is to pass over, around, and between an abundance of concrete and asphalt. These and other impervious, heat-absorbing surfaces provide little shade and no moisture compared to natural landscapes. They absorb heat throughout the day and release that heat well into the night. The city hums with vehicles, air conditioners, and other machines of comfort and industry, which give off a heat of their own into the urban environment, along with greenhouse gas emissions. The collective absorption, retention, and emission of heat create what is known as an urban heat island (or UHI). Think about how the street is hotter than the lawn on a summer day; cities are considerably warmer than the surrounding environment, often by an average of four degrees Fahrenheit in the daytime and three degrees Fahrenheit at night. This temperature difference varies within a city since trees, greenery, and heat-absorbing pavement and buildings lack even distribution.


Humidity is an exacerbating factor. As hard as it was not to roll your eyes when you heard “it’s not the heat, it’s the humidity” for the seven-thousandth time this summer, it’s true. Humidity makes it harder for sweat to evaporate, which you may recognize as how the human body cools itself. To take a wet bulb temperature, one wraps a damp cloth around the bulb of a thermometer as a way of approximating human skin. When the water evaporates, the thermometer cools, and the wet-bulb temperature is lower than the air temperature. When it’s humid and there is already moisture in the air, the water (sweat) has a more challenging time evaporating and cooling the thermometer (our body). In this case, the wet-bulb temperature is hotter than the ambient temperature. It can be dangerous to be outside doing physical activity too long because you’re at a higher risk of overheating. Navy folks know this as a “Black Flag” day. As the planet warms, dry areas will get drier, and wet areas will get wetter, which means Norfolk can look forward to even hotter, more humid days. 


UHIs have many negative impacts on human health and wellbeing. Besides being uncomfortable and irritating, excessive heat can cause respiratory trouble, cramps, heat exhaustion, heatstroke (non-fatal), heat stroke (fatal), and death (the most fatal). Our bodies are surprisingly fragile, and heat can place a tremendous amount of stress on them. Those “lazy days” of summer often occur because it’s just too hot to do anything but seek the shade comfortably. Meanwhile, nights are trending warmer, shortening the reprieve people can get from high daytime temperatures. Average nighttime temperatures are rising at a faster rate than average daytime temperatures. Darkness’ sweet embrace is losing the respite it once offered — higher nighttime temperatures mean that our bodies cannot cool as effectively, and the heat stress compounds and becomes a chronic stressor. 


UHIs are detrimental to air quality. We run the air-conditioner when it’s hot, and the hotter it gets, the harder we run it. Electricity demand for air conditioning increases as much as nine percent for every two-degree increase in temperature. This electricity is typically fossil-fuel generated, which emits greenhouse gases and other pollutants into the atmosphere. More greenhouse gases contribute to increasing temperatures, creating a positive feedback loop that keeps getting hotter.

Meanwhile, pollutants from power plants (and ACs, cars, and lawn-care equipment–remember we are in a city) create fine particulate matter and ground-level ozone. This matter is tiny (less than the width of a human hair follicle) particles that can be inhaled deep into the lungs. It may wreak all sorts of havoc, including decreased lung function, irregular heartbeat, heart attacks, irritated airways, sore throats, coughing, asthma, and general difficulty breathing. Ground-level ozone has similar health impacts.  


Certain groups of people are susceptible to the health impacts of heat and poor air quality: older adults, young children, low-income communities, people who work outdoors, people already in poor health, and of course, people who live in the city’s hotspots, where hyper-local temperatures are higher than that of the city overall. Many of these characteristics overlap, compounding people’s exposure and risk. Likewise, people who live in urban hotspots, these islands within islands, have to run their ACs more, running up their electricity bills. They see a choice between “run your AC and maybe not be able to pay your power bill” or “don’t run your AC to save money, and maybe be hot to the point of illness or death.” These burdens are not shared equally within a city due to the spatial distribution of roads, buildings, businesses, infrastructure, trees, parks, and open spaces. 


Where are these urban hotspots? In places with large amounts of paving and hard surfaces, with few trees or other vegetation. Areas with lots of vehicle traffic, industrial and commercial uses near residential uses, convenience stores, pawnshops, and payday lenders.  


Redlining is the practice of denying home loans or insurance to people living in too risky (“too not-white”) neighborhoods for investment. Illegal today, it was common practice in the 1930s through 1960s. Its namesake stems from the literal red ink on neighborhood maps from the government-backed Home Owners’ Loan Corporation (HOLC). Look at old insurance maps of Norfolk and compare them to the economically distressed neighborhoods of today — the overlap is remarkable (for further perusal, the Urban Renewal Center has an excellent Storymap


UHIs didn’t emerge by chance. In the 1950s, a burgeoning highway system, school segregation, and backlash against neighborhood integration saw Norfolk pour concrete along poor, majority-Black, neighborhoods to uphold racial segregation along urban corridors. For example, Fort Norfolk, present-day Atlantic City, was a growing racially integrated neighborhood in 1955. However, amid a national push for school integration, the Norfolk Redevelopment and Housing Authority demolished much of Fort Norfolk and its integrated school zone. They poured an industrial park into its place. Today, EVMS stands where Fort Norfolk used to be.


All that concrete broke up integrated neighborhoods and kept Black communities from expanding into white areas in Western Norfolk. In the move to demolish Fort Norfolk, the NRHA simultaneously widened Brambleton Ave. Norfolk would eventually see done with I-264 and Church Street to stop growing Black neighborhoods encroaching on predominately White communities. Hemmed in by concrete, today, historically poor Black areas have to contend with concentrated poverty and segregation, and concentrated heat.


Research from VCU and CNU bears this out. A paper by Jeremy Hoffman et al., published last year in Climate, examined the summer air temperatures across 108 different US cities. They found that in Hampton Roads, formerly redlined neighborhoods were, on average, 5.5 degrees hotter than neighborhoods that rated as most desirable (coincidentally colored green or blue) on the 1940 HOLC maps. A report by John Finn, CNU professor, and student research associates, shows that Norfolk neighborhoods redlined in 1940 have less tree canopy, more impervious surfaces, and higher temperatures than neighborhoods that were not. 


Telephone poles and street signs should not be a neighborhood’s only source of shade. The disparate impacts of redlining, urban heat, and poor air quality should not be ignored and left unaddressed. Increasing the urban tree canopy brings multiple benefits and should focus efforts on the neighborhoods that have been left behind since the 1940s. The City of Norfolk set a goal in 2009 to have a 30% urban tree canopy by 2040. According to nonprofit American Forests, a 4% increase in urban tree canopy would be a substantial achievement considering Norfolk’s urbanization. SB1393 will allow localities to require more than the minimum tree and landscaping requirements for specific development projects. Imagine its potential to rectify heat island impacts in vulnerable neighborhoods and advance environmental justice: development is typically cheaper in and around these communities. It often brings negative aspects like increased impervious surfaces or businesses that create more emissions. With authority granted by SB1393, Norfolk could require these businesses to plant more trees than they would otherwise have to by ordinance, which could mitigate the impacts of their activities; this would not undo the damage of years of disinvestment and neglect, but it could be a start. And as we previously established, trees are rad.



Sources & More Information:

“Will Factories Get Nod Over Homes at Village?” New Journal and Guide (1916-2003), May 14, 1955. Cf. Forrest R. “Hap” White, Pride and Prejudice School Desegregation and Urban Renewal in Norfolk, 1950-1959, (Westport: Praeger, 1992) |

Jeffrey Jeremy Hoffman, et al. The Effects of Historical Housing Policies on Resident Exposure to Intra-Urban Heat: A Study of 108 US Urban Areas. (Climate: Special Issue “Survivability under Overheating – The Impact of Regional and Global Climate Change on Vulnerable and Low Income Population,” 2020)

Littlejohn, et al. Elusive Equality: Desegregation and Resegregation in Norfolk’s Public Schools (Charlottesville: University of Virginia Press, 2021)

John Finn, et al. Living Apart: Report on 21st Century Segregation in Hampton Roads, Virginia. Christopher Newport University, 2021. 


Catie Sauer

Ghent, NFK

Catie was born in Norfolk and as an adult has lived here for two years and change. She has a master's in Environmental Planning and Design from the University of Georgia. She likes hiking, playing trivia, being a flaneuse, pinball, memes, and growing vegetables. 

Alex Fella

Alex Fella is a writer and researcher, his work focuses on the built environment and the natural world. He is the Director of Research at a Norfolk nonprofit and a 3rd year fellow at the Canadian Psychoanalytic Society. He has a master's in Philosophy from Yale University. He enjoys fixing old cars and rooting for the Montreal Canadiens.

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