Hot town, summer in the city: a look at heat islands
An estimated 739 people died from extreme heat over five days in Chicago during the summer of 1995.
Most of the victims were elderly and lower-income. They couldn’t afford air conditioners and reportedly avoided opening their windows for fear of crime.
Daytime temperature highs hit 106 °F (41 °C) that week. During the night, temperatures sat around the high 70s and low 80s—unusually high for Chicago. Overnight temperatures were also kicked up another couple of degrees by an urban heat island.
Not a shadow in the city
An urban heat island forms because of the high-concentration of buildings and pavement in urban areas. Buildings, concrete and pavement absorb more heat during the day and radiate more of that heat during the night into the immediate atmosphere.
Basically, cities get hotter than their surrounding rural areas and stay hot longer.
Extreme heat has detrimental effects on human health—no matter whether you’re living in an urban or a rural setting. However, urban heat islands cause additional risks to a community’s health, collective wellbeing, and surrounding environment.
Let’s take a look.
Increased energy demand
According to the U.S. Environmental Protection Agency (EPA), as people try to stay cool at work and home, “peak urban electric demand increases 1.5 to 2 percent for every 1°F (0.6°C) increase in summertime temperature.”
The demand on a city’s energy grid during a heat wave—and under a heat island— can (and has) led to power outages, which in turn, affects everything from a city’s infrastructure to its productivity.
Ozone and pollutants
“Elevated air temperatures increase the rate of ground-level ozone formation, which
is produced when NOx and volatile organic compounds (VOCs) react in the presence of sunlight,” explain EPA researchers. Ground-level ozone has a detrimental effect on human health, and can reportedly cause respiratory issues in children, such as asthma.
One study cited by the EPA showed that runoff from urban areas was typically 20-30°F (11-17°C) hotter than runoff from a nearby rural. As stormwater hits the various surfaces, it heats up and drains into sewers, which then raises the temperature of surrounding streams, rivers and lakes.
Another study in Arlington, Virginia, recorded temperature increases in surface waters went as high as 8ºF (4°C) in 40 minutes after heavy summer rains. According to the EPA, rapid temperature changes can negatively affect aquatic life. Hot, stagnant water, meanwhile, is perfect for breeding disease-causing bacteria.
Living together means building together
Urban heat islands are just another reason we need to build better buildings. Here at BASF, we’ve developed products like Elastopave®, a binder product that will not hold and absorb heat like conventional pavement materials. We have also developed a range of pigment solutions and other reflective materials that help mitigate solar heat. And we’re continually looking for new ways to develop and improve the products and materials that go into our shared buildings and streets.
But what we do at BASF is only one piece of the puzzle. To mitigate the effects of urban heat islands, it also requires designing projects with trees and greenery, and planning city infrastructure and development with an eye open for population growth.
In cities, we all live together. We must continue building together.