Cooling Effects of Street Trees In The Urban Heat Island (uhi) of Charleston, Sc

Charleston comes from its rapid growth in population causes adverse effects in its UHI, or Urban Heat Island. This UHI phenomenon occurs when an urban area, such as Charleston, is warmer than that of surrounding, rural areas. The peninsula of Charleston fosters buildings near one another, inciting more heat from shops, restaurants, and other businesses [1]. Temperatures in UHI’s are higher at night than they would be during the day because of the heat trapped by taller buildings at the ground-level [1]. Climate change is induced by the creation of these urban heat islands. Because of Charleston’s rapid growth, the city experiences changes in climate through its rising sea levels and increases in flooding. Since 2015, Charleston has seen 318 floods, with 2019 producing 89 of them [2]. To analyze the effects of the UHI in Charleston, temperatures, relative humidity, and dew points are collected through mounted HOBOware sensors. These sensors are on the southernmost side of Hampton Park, on Moultrie St. Each sensor is equipped with a solar radiation shield to negate the impact of direct sunlight to the sensors. Two common street trees in the area, the crepe myrtle and the live oak tree, are evaluated to find differences in the cooling effects of each tree. Street trees have proven to decrease the air temperature of the nearby area but increase the relative humidity. Data collected from the Bluetooth sensors are compiled into graphs and plotted against each other to determine whether one tree is more effective than the other tree. A comparison of temperatures over the hottest day in the month of August. The live oak is warmer than the crepe myrtle from 0630 to 1030 and from 1200 to 1430 the crape myrtle was warmer than the live oak. Changes in temperature and relative humidity are placed into the Rothfusz regression to get a heat index. The heat index gives a better indicator of the body’s perceived temperature or the “Feels Like” temperature. The heat indices for these trees are relatively similar. The average crape myrtle heat index is 36.08°C and the average live oak heat index is 35.93°C. No statistical significance was found when comparing the heat index of the trees, but correlations can be derived. As the air temperature increases, the relative humidity increases. These findings are significant in the scope of reducing the UHI of Charleston because of the ability for street trees to decrease the air temperature. Although implementing more trees would reduce the air temperature, it would not impact the heat index because of the correlation between the two variables. More research could show that street tree findings could prove useful for city planning in cities experiencing growth. We plan to mount more sensors along Moultrie St., close to Hampton park. An increase in sensors could provide more statistically significant data regarding the location of the new trees.

1. https://www.nationalgeographic.org/encyclopedia/urban-heat-island/ 2. https://www.weather.gov/chs/coastalflood