Our Cities Are Getting Hotter
Cities across India are increasingly becoming ‘urban heat islands’, a phenomenon where metropolitan areas are significantly warmer than surrounding rural areas. This is largely because our cities are dense jungles of concrete and asphalt. Traditional
dark-coloured roads and roofs absorb anywhere from 80% to 95% of the sunlight that hits them, storing this energy and releasing it as heat, which pushes temperatures higher. This effect is particularly pronounced in India, where the frequency of heatwaves is on the rise, making urban living increasingly stressful and dangerous.
What Are Cool Pavements?
Enter cool pavements. The concept is simple and acts much like wearing a white shirt instead of a black one on a sunny day. Cool pavements are surfaces made from materials that reflect more sunlight and absorb less heat. This can be achieved in a few ways: using lighter-coloured concrete mixes, applying a reflective coating to existing asphalt, or using permeable materials that allow water to evaporate and cool the surface. The key metric here is ‘solar reflectance’ or ‘albedo’—the higher the value, the more sunlight is reflected away, keeping the surface from heating up.
Proven Results in India and Abroad
This isn't just a theoretical concept; pilot projects have demonstrated tangible results. In cities like Phoenix, Arizona, applying a reflective coating has been shown to lower midday pavement surface temperatures by as much as 10-12°F (about 5.5-6.7°C). Encouragingly, Indian cities are also testing this technology. A project in Hyderabad using high-reflectance concrete lowered surface temperatures by up to 14°C. Ahmedabad’s trials with various cool pavement types reduced ambient air temperatures by 2-5°C, while a large-scale project in Chennai saw ambient temperatures drop by 3°C.
The Broader Benefits of Staying Cool
The advantages go beyond just a cooler street. Lower ambient temperatures mean less demand for air conditioning, leading to significant energy savings and a reduction in greenhouse gas emissions. For example, even a one-degree reduction in a city's average temperature could lead to millions in annual savings from avoided AC costs. Cooler pavements can also improve air quality by slowing the chemical reactions that form smog. Furthermore, the reflective surfaces can enhance nighttime visibility, potentially reducing the need for extensive street lighting and saving more energy.
Challenges and Considerations
Despite the promise, cool pavements are not a perfect solution. One of the primary concerns is cost. The special coatings and materials can be more expensive than traditional asphalt, though some estimates place the difference as marginal. There is also the issue of glare; a highly reflective street could be uncomfortably bright for pedestrians and drivers, similar to a sunny day on fresh snow. Another study noted that while the pavement itself is cooler, the reflected radiation could actually make pedestrians feel hotter. Finally, the effectiveness of the coatings can degrade over time as dirt and traffic wear them down, requiring maintenance to retain their reflective properties.
