Resilience within city planning has become increasingly important as global temperatures continue to rise; however, current inequities in localized temperature distribution pose an even greater need for innovative solutions regarding heat regulation.
Heat Islands refer to urban areas that are significantly hotter than surrounding rural areas. The relative increase of heat between the measurements of urban areas compared to that of suburban or rural areas around creates demarcations where heat islands start within a city. Additionally, areas within a city or urban area may be hotter within the heat island itself. These areas are referred to as intra-urban heat islands or hot spots.
There are various ways to measure a heat island for classification. For example, the Environmental Protection Agency, EPA, points to various studies that used the measurements of air temperatures throughout a city, while others used surface temperatures to demarcate heat islands. While both methodologies are valid, a combination of both are often recommended to fully assess the compounding causes of heat islands and hot spots within an urban area.
Lack of Reflective Surfaces: A common possible cause of magnified temperatures in urban areas has to do with the surfaces that urban areas are constructed with. Reflective surfaces allow the Sun's rays to be redirected off the surface of buildings, sidewalks, and roads, which limits the amount of heat that stays. However, objects in urban areas are often constructed with materials like asphalt and concrete that absorb solar heat rather than reflecting it. This increases the amount of heat felt in cities that are planned with entire zones that overuse these materials in their blocks and buildings. For example, in Maricopa County, Arizona, residents suffered severe burns because of the absorbing effect of the asphalt on parking lots and roads.
Reduced Natural Landscapes: In most urban areas, few spaces include greenery or natural landscapes. This landscape change poses two main threats: lack of shade and lack of moisture. Firstly, trees and other large greenery that exist within green areas, such as parks, create lots of shade that mitigates the effects of high temperatures. However, the reduction of these areas decreases the shade outside. Additionally, grass and other soil-based foundations easily store water that allows it to be kept and later released into the atmosphere; however, a lack of these permeable, or water-accepting, foundations forces water to flow out of the city as runoff into other ecosystems which decreases the moisture in the air and atmosphere that help cool the area.
Geometric and Geographic Difficulties: An additional issue caused by current city designs includes a lack of air circulation. In suburban and rural areas, wind can circulate hot air and naturally cool the area. However, the height of buildings in urban areas and their close proximity to each other in many cities prevent the ability for wind to circulate in the area, denying the area access to the cooling method. Furthermore, in some cities large mountain ranges can give a similar effect and block currents of wind.
Anthropogenic Causes: Human actions may also exacerbate the issue and lead to increased heat and worsened heat magnification. Large energy use through things like vehicles, home appliances, and electronics causes the release of pollutants such as methane that create a "greenhouse gas effect". After the Sun's rays are reflected off the Earth's surface, they get trapped by the thick layer of pollutants released, and the heat gets trapped near the surface of the Earth. Though this phenomenon is not exclusive to urban areas, the effects are often increased and magnified due to the population density that exists within cities.
Multiple harms are inherent to heat islands, such as heat exhaustion, overheating, and in some cases, death. While these harms are reason enough to be concerned with the threat that heat islands and hot spots pose, there are additional reasons that heat islands should cause concern for residents within cities. The demographic skews for what groups of people are more likely to experience heat islands make them an issue of environmental injustice. A study done by Angel Hsu, an associate professor and researcher at the University of North Carolina-Chapel Hill, found that in 169 out of 175 major US cities measured a person of color had a higher surface urban heat island (SUHI) intensity than that of a white person. The public health and safety concerns posed by the threat of heat islands and hot spots on already vulnerable and marginalized communities call for innovative solutions to solve this urgent, and increasingly dangerous, problem.
Though the problem of heat islands and hot spots is caused by a connection of complex factors, the solutions proposed by the EPA to mitigate their heat magnification are quite simple. Firstly, the EPA recommends that cities add green spaces to their infrastructure. This helps create shaded areas and adds moisture to the area to decrease the temperature. Additionally, innovative green spaces such as "green roofs" or gardens housed on the roofs of urban buildings can also reduce the amount of heat-absorbent materials that are directly exposed to the Sun. Furthermore, the use of reflective surfaces such as white colored surfaces and polished metals can help to reduce the amount of solar heat that an urban area consumes and traps. Replacing standard concrete with white concrete and introducing designs that incorporate metal into the exterior of buildings are all effective ways to possibly reduce the effects of heat islands and hot spots.
Heat islands and hot spots pose a significant threat to the function of cities and the quality of life for the residents within them. While there are individual ways that certain design choices and planning strategies have created heat island effects, oftentimes a combination of factors compound on each other to increase the temperature of urban areas. As global temperatures rise with the widespread impacts of the greenhouse gas effect, heat islands exacerbate the issue and create a serious concern for city planners, legislators, and community advocates. Implementing solutions to solve heat absorption can help to solve the issue at its root, ensuring that heat is not initially trapped in urban settings and cannot be compounded in the first place. While simple solutions such as green roofs and white concrete cannot shield residents of cities from the severe, impending increase of heat, they can act as mitigators to the harsh conditions faced every day by those who live in heat islands and hot spots, who feel the effects of global warming the most.