It is no surprise that highly urbanized areas with little vegetation cause negative effects on their inhabitants and the local climate. These areas are called heat islands, and can be 1–7°F hotter during the daytime and 2-5°F hotter at night in comparison to more natural, vegetated land. There are two main factors that contribute to heat islands: the loss of vegetation that naturally provides cooling and the man-made structures that lead to retention of heat.
Natural growth provides shade, which cools the land in its shadow. Trees also cool the air as the water in their leaves transpires. Bodies of water which may be covered or diverted in urban areas would also cool the air if left untouched.
The building materials themselves in urban areas retain more heat than plants do, contributing to the rise in temperature within heat islands. Large man-made structures such as several-story buildings can also block the flow of wind, which would normally have a cooling effect in the city. These temperature differences are also greater in areas of denser populations. Increased human activity leads to increased use of all sorts of machinery, electronics, vehicles, and other industrial innovations, which all release thermal energy into the environment [1].
Not only are heat islands associated with increases in temperature, they can also be costly—in terms of energy, household electricity cost, and government aid. When the temperature rises in an urban area, it can cause a strain on power grids as more people use electricity to cool their homes. This leads to an energy loop, where people use electricity to cool their homes, which releases thermal energy out into the environment, which thereby makes the heat island even worse [2].
The environment also suffers because of these heat islands, because all parts of an ecosystem are interconnected, both biotic and abiotic. If the bodies of water in a heat island are heated and then flow into local rivers or lakes, it can cause harm to animals living there that have adapted to live in a cooler environment. Pollutants in heat island cities also have more severe effects, as they cannot easily be dispersed; air pollutants cannot be blown away due to disrupted air flow by tall buildings, and ground-level pollutants do not go down into the earth due to man-made non-permeable materials like roads and sidewalks [2,3].
These heat islands can also affect human health. “[Urban heat islands] intensify health problems in cities,” writes Professor Mattheos Santamouris, author of several books on heat islands and energy conservation, “During the 2003 heat wave in France, the excess mortality in Paris surpassed 140%, while in smaller cities it was much lower at close to 40%” [3]. Heat related illnesses like heat stroke and respiratory difficulties can be severe, and even fatal, especially in certain populations. Those who are very old or very young, those who have preexisting health issues, and those who work outside can be susceptible to increased effects from heat waves.
Two final demographics of people who are more severely affected by heat islands stress the lack of equity in this environmental issue. Those who are low-income, and people of color.
Per a 2021 research study on disproportionate heat island intensities, “We find that the average person of color lives in a census tract with higher [Surface Urban Heat Island] intensity than non-Hispanic whites in all but 6 of the 175 largest urbanized areas in the continental United States,” [4]. This disparity is theorized to be partially due to historical redlining—the denying of home sales or loans based on the area’s racial makeup. The data shows that these redlined, historically POC neighborhoods have a higher temperature makeup than other neighborhoods within the same city [4]. This racial segregation can lead to lack of funding and neglect by the local government, and “leads to people of color incurring more environmental health risks, including higher levels of exposure to pollution, hazardous waste, and urban heat” [5].
Low income households also face inequitable consequences from heat islands. The effects are dissimilar to the experiences of POC—“In nearly half the urbanized areas, the average person of color faces a higher summer daytime [Surface Urban Heat Island] intensity than the average person living below poverty”—but are still very significant [4]. Low income households are more likely to have a lack of air conditioning and shelter, and thus are more susceptible to inequitable heat related illness and death during hotter months [6].
Systems must be implemented in order to decrease the amount and severity of heat islands, as well as give additional help to demographics most affected by heat islands. Planting vegetation in the ground or on rooftops, as well as using lighter colored materials on buildings are two simple ways to help improve heat island intensity, but there are many more solutions out there that researchers are studying and implementing [2]. As this is a form of local climate change, it is up to local governments to notice and take charge when their communities begin to experience severe heat island effects. It is also important for governments to understand and recognize the inequitable effects of heat islands and to make sure all of their citizens are given aid and funding to help heal these local climate issues.
References:
1: Learn About Heat Islands. (2022, September 2). US EPA. Retrieved October 9, 2022, from https://www.epa.gov/heatislands/learn-about-heat-islands
2: Urban Heat Island | National Geographic Society. (n.d.). Retrieved October 9, 2022, from https://education.nationalgeographic.org/resource/urban-heat-island/
3: Santamouris, M. (2019). Urban Heat Island and Local Climate Change. In Minimizing Energy Consumption, Energy Poverty and Global and Local Climate Change in the Built Environment: Innovating to Zero. Elsevier. https://doi.org/10.1016/B978-0-12-811417-9.00003-9
4: Hsu, A., Sheriff, G., Chakraborty, T. et al. Disproportionate exposure to urban heat island intensity across major US cities. Nat Commun 12, 2721 (2021). https://doi.org/10.1038/s41467-021-22799-5
5: Ndugga, N., & Artiga, S. (2021, September 8). Extreme Heat and Racial Health Equity. KFF. Retrieved October 9, 2022, from https://www.kff.org/policy-watch/extreme-heat-racial-health-equity/
6: Heat Island Impacts. (2022, September 2). US EPA. Retrieved October 9, 2022, from https://www.epa.gov/heatislands/heat-island-impacts