Chicago summers are getting harder to sit through, and a six-day heatwave in August 2021 gave scientists a real-world test case. In a new study published in Science of the Total Environment, researchers at Argonne National Laboratory modeled the effects of replacing all rooftops in the Chicago metropolitan area with a cooler surface. The results were notable. Using white cool roofs lowered near-surface air temperature by an average of 1.5 degrees Celsius across the metro area, and cut cooling energy demand by 16.6 percent on average.
How scientists tested a fix for an entire city
Most previous cool roof studies have been limited to a single building or small neighborhood. Haochen Tan, an atmospheric scientist at Argonne, and his team wanted to see what would happen if the concept were scaled up to an entire metro area. The study notes that they used a Weather Research and Forecasting model, a tool climate scientists use to simulate weather in great detail for specific regions, and applied it to the real August 2021 heatwave. Instead of just imagining the effect, they simulated three real scenarios across every building in the region: roofs that were white and reflective, roofs covered in vegetation, and roofs fitted with solar panels.
White roofs came out ahead
Cool roofs proved to be the most effective option by a long shot. The air around them stayed cooler through the day because white surfaces reflect more sunlight instead of absorbing it as heat. That was a reduction of about 1.5 degrees Celsius in near-surface air temperature and a 16.6 percent reduction in the energy needed to cool buildings, averaged across the metro area, per the Argonne research summary. However, there is a limitation. Cool roofs can lose some of their shine, literally, as dirt and weathering build up over the years, which can chip away at their performance if not maintained, the research notes.
