What is Urban Heat Island effect and how your car colour may impact city temperatures
A University of Lisbon study reveals that parked cars significantly contribute to the urban heat island (UHI) effect. Dark-coloured vehicles absorb and radiate more heat than lighter ones, increasing ambient temperatures, especially in densely populated areas. This intensifies the already heightened temperatures in cities due to materials like asphalt and concrete. The study highlights the importance of considering vehicle colour in urban planning to mitigate the UHI effect.
New Delhi: Heat emitted from parked vehicles, especially those in darker colours, is quietly pushing up urban temperatures more than previously thought, adding to the already dangerous urban heat island (UHI) effect.
A recent study by researchers at the University of Lisbon reveal that the colour of a vehicle can have an effect on the temperature of the air around it in a big way.
The research highlights the UHI effect, a phenomenon where cities remain consistently warmer than the surrounding rural areas.
How urban heat island (UHI) effect is caused
The UHI effect takes place when city environments absorb and retain heat. This heat is caused by human-induced activity and the widespread use of materials such as asphalt, concrete, and steel. These materials absorb heat very fast under direct sunlight and emit it slowly. This leads to higher temperatures that continue to stay in the night. At night, cities can be 10°C warmer than the adjoining rural regions. The difference in temperature becomes more stark during the summer months, when the intensity of the sun is highest.
In places with dense construction, there's limited flow of air. This increases the heat in the day. Besides, vehicular traffic, industrial activities, and uncontrolled use of ACs go a long way in warming the temperature further.
During the night, rather than cooling down, streets, rooftops, and infrastructure in the cities emit the heat they have stored. Therefore, there's no respite from the day’s high temperatures even at night.
The UHI effect poses more risks during heatwaves. In Europe, where almost 70% of the population resides in urban areas, the UHI effect is fast emerging as a significant public health issue. London, Paris, Rome and many other cities have been witnessing heightened night-time temperatures in recent times.
How cars add to the urban heat
The University of Lisbon study highlights the role parked vehicles play in contribute to the heat and the UHI effect. The research examined and explored how vehicles respond to and interact with their adjoining areas under intense sunlight.
The study revealed that when parked in open areas, the surfaces of vehicles can hugely affect local temperatures -- particularly in dense urban centres where cars occupy a huge road space.
Márcia Matias, who led the Lisbon research, said: "Now picture thousands of cars parked across a city, each one acting like a little heat source or a heat shield. Their colour can actually shift how hot the streets feel.”
What the researchers did and what they found
The researchers put two cars — one black and one white — under a clear summer sky with a temperature of 36°C. After five hours of direct sunlight, the air temperature surrounding each vehicle was recorded.
And the findings were startling. The black vehicle raised surrounding air temperatures by up to 3.8°C more than that of the nearby asphalt road, whereas the white car caused a far smaller spike.
It brought to the fore how differently colours interact with sunlight. Vehicles with light colours reflect 75 per cent to 85 per cent of incoming sunlight, which limits the heat absorption. Those which are dark reflect only 5 per cent to 10 per cent of sunlight, absorbing the rest and heating up faster.
Unlike asphalt, which is thicker and heats up more slowly, a car’s thin metal body warms faster. After it is hot, it radiates heat into the surrounding air. This creates small but intense zones of higher temperature.
When added up across a city, with thousands of vehicles on the streets and in the parking areas, these individual heat sources can combine to raise urban temperatures, essentially in already heat-stressed pockets.
If dark-coloured vehicles are repainted in lighter shades, it could enhance street-level reflectivity from 20% to nearly 40%. This could go a long way to noticeably cool the air just above the surface under sunny, low-wind conditions, the study found.