Urban Dark-Colored Vehicles Act as Mini Heat Sources, Contributing Significantly to Raising City Street Temperatures Several Degrees
In a groundbreaking study published in City and Environment Interactions, researchers have identified parked cars, particularly dark-colored ones, as a significant contributor to urban heat islands. The study, led by Sarah Berk, a climate researcher at the University of North Carolina, challenges the traditional way of modeling city temperatures.
The study, which took place in Lisbon, Portugal, counted over 91,000 street parking spaces and more than 700,000 cars circulating through the city on a typical weekday. The researchers found that the physical presence of parked cars can be just as impactful as buildings in city temperatures.
Cars heat up quickly and radiate heat outward into the surrounding air. Unlike asphalt, cars are made of thin sheets of steel or aluminum that heat up rapidly. In an experiment in Lisbon, a black car heated the nearby air by 3.8°C more than the asphalt beneath it, while a white car had a smaller effect.
The difference in temperature is due to the physical properties of the car colors: black absorbs more heat than white. Black paint reflects only about 5 to 10% of incoming sunlight, while white reflects up to 85%. This means that light-colored vehicles, such as those commonly found in cities like Los Angeles, Phoenix, and Dubai, can enhance the albedo effect by reflecting more sunlight and thus helping to reduce urban heat islands.
The study highlights the role of parked cars as a new culprit in urban heat islands, adding to the list of factors that raise city temperatures. City planners could potentially combat this issue by incentivizing light-colored vehicles in heat-prone zones, installing shade structures in parking areas, encouraging the use of reflective coatings on cars, and considering color-based parking restrictions in critical areas.
Moreover, the effect of multiple parked vehicles across a city could lead to noticeable shifts in air temperatures in entire neighborhoods. A switch from dark to light-colored vehicles in areas where parked cars cover 10% or more of the road surface could increase solar reflectivity by up to 19 percentage points, with tangible cooling potential.
The authors of the study note that their findings are a snapshot, not accounting for seasonal shifts, cloud cover, or the growing presence of electric vehicles. However, the study does not account for the growing presence of electric vehicles in the analysis, a factor that could potentially mitigate the impact of parked cars on urban heat islands in the future.
Sarah Berk, the lead researcher, commented that most urban heat strategies focus on rooftops and pavements. Harnessing light-colored vehicles as a mitigation strategy for urban heat is particularly novel. The study in Lisbon demonstrates that this approach could potentially be a simple solution to reduce the effect of parked cars on urban heat islands.
In conclusion, the study published in City and Environment Interactions reveals that parked cars, especially dark-colored ones, can contribute to urban heat islands. By understanding this impact, city planners can take steps towards mitigating the problem and creating more sustainable, cooler cities.
