Modern cities, with their concrete sidewalks, black asphalt streets, and brick and steel buildings, have long been associated with the urban heat island effect. This phenomenon refers to the retention of heat by these city elements, leading to increased temperatures within urban areas. As summer temperatures continue to rise, it has become crucial for cities like Chicago to equip decision-makers and communities with strategies to help keep residents cool. One of the strategies that have gained attention involves utilizing rooftops. In particular, certain roofing materials have the potential to cool the surrounding air and reduce the need for air conditioning. Researchers at the U.S. Department of Energy’s Argonne National Laboratory have examined three different roofing strategies to assess their impact on near-surface temperature and cooling energy demand in the Chicago metropolitan area.
The researchers conducted regional modeling to evaluate the effects of three types of roofs: cool roofs (heat-reflecting white roofs), green roofs (vegetated roofs), and solar panel roofs. To maximize potential benefits, the study was conducted during a heatwave event, where temperatures exceeded the 95th percentile observed in the city for three consecutive days. The regional climate model simulated the Chicago metropolitan area, and the results demonstrated the impact of each roofing strategy on near-surface temperature and air conditioning consumption during the hottest hours of the day.
Based on the research findings, it was observed that all three types of roofs contributed to reduced near-surface temperatures and decreased cooling energy consumption. Cool roofs exhibited the most significant cooling effect, reducing the near-surface temperature by 1.5 degrees Celsius. Green roofs followed closely with a reduction of 1.2 degrees, while solar panel roofs showed the smallest reduction of 0.6 degrees across the Chicago area.
In terms of cooling energy consumption reduction, cool roofs outperformed both green roofs and solar panel roofs. The implementation of cool roofs led to a 16.6% reduction in energy demand, followed by a 14.0% reduction with green roofs and a 7.6% reduction with solar panel roofs. Additionally, cool roofs proved to be more cost-effective when compared to the other two technologies. They were less expensive and did not require additional water. However, it is important to note that green roofs have an added advantage in managing stormwater loads, which cool roofs lack.
The results of this research can be used by stakeholders to inform sustainable development approaches and reduce cooling energy demand during the summer months. By deploying the recommended roofing strategies, cities like Chicago can also aim to minimize greenhouse gas emissions in the long term. This study was part of the Community Research on Climate & Urban Science (CROCUS) Urban Integrated Field Laboratory, which focuses on understanding urban climate change and its implications for environmental justice. The findings serve as a baseline for CROCUS communities and provide valuable insights for planning and testing mitigation options.
Building upon these findings, the researchers aim to develop city-scale and global-scale models for each of the roofing options. To do so, they will work on improving data collection and understanding of green roofs. Measurements at surface and building levels will aid in refining calculations and models. The team plans to measure the roofs of CROCUS partners throughout Chicago, including those with green roofs and solar panels. To enhance the resolution of the model, researchers aim to incorporate street-scale data, which will help differentiate between the cooling effects of trees on buildings and pavements. Achieving this level of detail is essential for accurately assessing the impact of various interventions.
To conduct this extensive research, the team utilized the supercomputing resources at the Argonne Leadership Computing Facility (ALCF) and the National Energy Research Scientific Computing Center (NERSC). These facilities are user facilities of the DOE Office of Science located at Argonne National Laboratory and Lawrence Berkeley National Laboratory, respectively. By harnessing the power of supercomputing, researchers were able to run complex simulations and generate valuable insights into the cooling effects and energy savings associated with different roofing strategies.
The research conducted by the scientists at Argonne National Laboratory sheds light on the potential of utilizing different roofing strategies to combat the urban heat island effect in cities like Chicago. By adopting and implementing cool roofs, green roofs, or solar panel roofs, cities can significantly reduce near-surface temperatures and cooling energy consumption during the hottest hours of summer days. These strategies not only offer environmental benefits but also contribute to sustainable development and the long-term reduction of greenhouse gas emissions. As the study continues, further research will refine the models and provide decision-makers with more precise insights into the cooling benefits of each roofing option. With ongoing advancements in technology and the commitment of researchers, cities can explore innovative strategies to mitigate the urban heat island effect and create a more sustainable and livable environment for their residents.
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