One of the most noticeable and deadly consequences of global climate change is the intensity of urban heat islands. These are built-up areas with temperatures that are higher than the rural areas that surround them. Cities with over 1 million people can be 2 to 5 °F hotter than neighboring areas. Accompanied by escalating heatwaves, these concentrations of high temperatures can foster an environment which is detrimental to public health. In 2018, extreme heat was the number one cause of weather-related deaths, outnumbering fatalities caused by hurricanes, floods and tornadoes combined.
Several factors can create heat island conditions. Cities with grid-like layouts trap air flow, and a lack of vegetation and green spaces also contribute to blistering temperatures. Further, a high proportion of urban elements like heavy roofs, and pavement in the form of driveways, roads and sidewalks without tree coverage add to the effects. It is in these ‘concrete jungle’ environments that the urban heat island effect is most severe. Heat islands can amplify uncomfortably hot summer days to become dangerous and life threatening. One of the most dangerous aspects of heat islands is that they prevent cooling during the nighttime, meaning there is no respite from the high temperatures.
Like most harmful effects of climate change, those who are already disenfranchised and vulnerable to other threats face the most perilous situation. The young and the elderly are more susceptible to health complications from the heat, as well as homeless individuals who don’t have access to cooling resources and are more likely to suffer from heat exhaustion and dehydration. Additionally, studies have shown a link between urban heat island conditions and residential segregation. Black Americans are 52% more likely to live in areas with heat risk–related land cover conditions than white Americans. Further, urban heat island “conditions increased with increasing degrees of metropolitan area-level segregation.” Residents of areas which experience heat islands effects are also likely to have high utility bills from running cooling systems.
There are several ways to design cities in ways that mitigate the effects of urban heat islands. Planting greenery on roofs can create a shade canopy that reflects more heat from the sun than a standard roof would. The type and color of materials used to make roofs and paved surfaces can also influence the amount of solar energy that is reflected rather than absorbed. Residents of Dallas, Texas used GIS mapping software to examine which areas of the city experience the greatest dearth of tree canopy coverage and have set out to plant over 1,000 trees, and report showed that the program could lead to a cooling effect of 15°F on hot days. A comprehensive approach to addressing urban heat islands necessitates environmentally focused community efforts, proper urban planning, energy efficient cooling systems and the breakdown of residential segregation in policy and in practice.
Sources and Further Reading
The Racial/Ethnic Distribution of Heat Risk–Related Land Cover in Relation to Residential Segregation – Environmental Health Perspectives
Cooling Dallas’s Concrete Jungle – City Lab
What Is the Relationship between Urban Heat Islands and Segregation? – How Housing Matters
Heat Island Effect – Environmental Protection Agency
Weather Fatalities 2018 – National Weather Service