Urban Heat Island Impacted By Tree Equity
Poverty-stricken neighborhoods lack vegetation when compared to higher income neighborhoods, creating a heat island effect.
The Industrial Revolution jumpstarted generated an increase in technological, medicinal, and ideological advances. Technological and ideological advancement created an opportunity for businesses to expand their operations. Instead of hand-sewing a pattern, a worker could use a sewing machine to efficiently make stitch a shirt. Instead of building a car from scratch, machines could now cut standardized pieces. This, along with the new ideological method of the assembly line, effectively reduced vehicle prices. Businesses tended to establish themselves close to areas where they could easily obtain freight. These locations were cities sat by water, where ships could dock. Expansion of businesses meant an expansion of jobs. This resulted in rapid expansion of the population in every major city as people emigrated from their rural homes. With an increase of medicine, new hygienic practices began to take hold, reducing the death rate. This contributed to an even rapid expansion. To keep up with the population increase, each city had to build new homes at a fast pace. Since they were worried about providing apartment complexes, there was little thought put into the design of the landscape.
Today, this is felt by people who still live in these complexes. The rush to store as many people in the smallest area possible did not think about incorporating vegetation, especially trees, into their design. As mentioned earlier, the price of cars dropped. This contributed to an increase of impervious surfaces as tar was laid over soil to provide a stable ground for vehicles. As all of this was happening, the rate of use in fossil fuel consumption jumped dramatically. Unbeknownst to humanity, this would increase the amount of carbon dioxide (CO2) in the air, leading to one of the biggest crisis we have yet to face, climate change. Climate change is the change in the Earth's overall average temperature. As the air's chemical composition changes, so does it's ability to hold the sun's solar radiation. According to the National Oceanic and Atmospheric Administration (NOAA), CO2 levels in 1960 used to be less than 320 parts per million (ppm), a concentration the Earth has not experienced in over 8,000 years. In 2020, the newest estimate placed CO2 at less than 420 ppm, an almost 100 ppm increase in 60 years. This has resulted in a net increase of one degree Celsius.
All of these factors has lead to an interesting phenomenon that is currently being studied in urban cities. With the warming of our climate, the poor landscape design of our cities, and the impervious surfaces lining our floor, it has created urban heat islands (UHI). Urban heat islands is exactly as it sounds. There are areas in a city where the average temperature is warmer than the rest of the surrounding area.
These temperature rises threaten vulnerable people who might not be able to adjust to the heat. Vulnerable people include, but are not limited to: children, elderly, and people in poverty. In a study done by Vanos et al., children do not have a functioning metabolism, which affects their ability to sweat. Their smaller bodies also means they have a higher volume to mass ratio. This makes them more susceptible to heat changes as they can absorb heat at a faster rate through osmosis. Elderly people, on the other hand, loss their ability to regulate their internal body temperature as they age, making them just as susceptible to extreme temperature changes. People in poverty have a different experience. They may not be able to avoid the air conditioning required to regulate their homes.
Mitigation strategies to reduce UHI affects are being researched every day. The main strategy I want to go over is the use of vegetation and tree equity. What is tree equity ? Tree equity is the amount of trees a neighborhood has. Research has shown that in neighborhoods with a low median income has little tree equity while the opposite is true for high median incomes. American Forests, an organization, has decided to calculate a tree equity score for cities across America and has built a website to allow easy access to the data.
The tree equity score reports how much shade is available to the neighborhood based on tree canopy coverage. The higher the score, the more shade there is. Trees, along with other vegetation, provide many beneficial roles to our communities. Shade prevents solar radiation from heating up the impervious surface, which is typically dark-colored and can hold heat for a long time. It also naturally reflects solar radiation back into the sky. The process of evapo-transpiration from plants releases water into the air, further cooling the surrounding environment. Vegetation is so effective that when comparing a map on vegetation to a map of UHI locations, UHI are stronger in areas where vegetation hardly occurs. In the maps below I will provide a real-life example of these concepts.
The above map is a small town called Frostburg, located in Allegany County, MD. he tree equity score for the city of Frostburg. The darker the blue, the higher the score for that area and vice versa.
In this map, it is a unique viewpoint on how a normal resident would divide the town up by income.
This is the median income of Frostburg. The data comes from Esri.
In this comparison there are several areas where they seem to contradict each other. Namely, the business sector, the bottom of Frost Village, and the Frost Elementary Territory. For the business sector, the heat island follows along main street. At the bottom of Frost Village, a giant parking lot is located there. The heat island in the middle of Frost Elementary Territory, there is two huge blacktops, one for a church and one for Frost Elementary. All of these are impervious roads that would be able to store up and retain heat from the sun. Another weird area is that there is no UHI in the area behind the community park. This could be due to the fact that there is not a lot of development in the area, and the houses all wrap around a large swath of forest. Unsurprisingly, the College Student Housing area has a wide UHI, and a low tree equity score. The student housing all are owned by companies. In general, trees can become a liability because of the possibility of them falling down and destroying private or public property (Siriwardena et al., 2016). Rental companies removing trees off the property do it to avoid future problems. This negatively affects the college students, though, since their homes will require more energy to cool off.
In this section, when comparing the median income to the UHI vs tree equity score, a spatial distribution pattern becomes evident. If you follow along main street, you begin to notice that lower median incomes as well as most of the UHI's are located on the left side. On the right side, income increases dramatically and UHI's exist in small quantities. This is most likely due to the development of the town. Where most of the UHI exists is the oldest part of Frostburg, the main district. Back in the day, the buildings in town was designed to be close together to allow people to travel from place to place. As suburban-themed towns became the mainstream, buildings began to be separated.
Observing the houses on the map give a perfect representation of this occurring. In almost every edge of Frostburg (Braddock Estates, Victoria Lane, Frost Elementary Territory, and the Area Behind the Community Park), the houses become more distant from its neighbors. This opens up a lot of land, leaving huge lawns full of grass. Most people also plant small trees in their front- or backyard to add aesthetic appeal. This would explain why those sections of Frostburg have little to no UHI's.
As climate change gets worse so will the UHI effect. Actions need to be taken to prevent unnecessary deaths. The best course of action is to incorporate vegetation into the city's structure. For example, plant more trees, advocate owners and rental companies not to cut down mature ones, install green roofs, push for public garden, so on and so forth. Since Frostburg is a small town, the effects of UHI are small in comparison to a larger city like Baltimore. Besides impacting the area in the summer, it would be interesting to see if UHI persists through winter time. If it does, it might be beneficial to the surrounding houses as it would keep them warmer. There is a chance it might trap the cold just as well as it does heat, which would increase electricity consumption in houses around the area. Unfortunately, there is little knowledge on what happens to UHI when wintertime begins.