White roofs most effective at cooling cities

Researchers from University College London have found that painting roofs white or adding reflective coatings, known as "cool roofs," is the most effective method for cooling urban areas like London. Using a three-dimensional urban climate model, the study demonstrated that if widely adopted, cool roofs could reduce outdoor temperatures by about 1.2 degrees Celsius on average, and up to 2 degrees Celsius in some locations. The research compared various urban heat management systems, including green roofs, street-level vegetation, rooftop solar panels, and air conditioning.

The study found that green roofs, while beneficial for drainage and wildlife habitats, provided negligible cooling effects, with erratic temperature patterns that could increase heat at night. Solar panels and street-level vegetation also contributed to cooling but to a lesser extent, averaging a reduction of about 0.3 degrees Celsius. Additionally, extensive use of air conditioning was shown to potentially warm the outdoor environment by up to 1 degree Celsius in dense city areas. The findings, published in Geophysical Research Letters, suggest that cool roofs could be a significant element of climate adaptation strategies in urban settings.