Given the significant contribution of the built environment to higher energy demands, GHG and air pollutant emissions, human health risks, and discomfort, etc., it has become increasingly crucial to develop feasible methods for reducing building energy use.  This study investigates the energy-saving potential of green roofs and cool roofs in reducing building energy consumption. Using an integrated approach that combines climate change modeling and building energy simulation, the study evaluates these strategies in six global cities (Cairo, Hong Kong, Seoul, London, Los Angeles, and Sao Paulo) under current and future climate change scenarios. 

Key findings:

• The energy-saving effects of cool roofs and green roofs largely depend on the climate zones in which they are implemented. Both roof systems demonstrate significant potential in reducing cooling energy demand across various climates, while the increase in heating energy demand associated with cool roofs should be considered in cities with colder climates.

• The energy-saving effects of cool roofs and green roofs are influenced by the urban built environment. The best energy-saving performance is observed in low-rise buildings, and as building height increases, there is a decreasing trend in energy-saving performance.

• In future scenarios with high greenhouse gas emissions (SSP 5–8.5), cool roofs and green roofs are expected to save more cooling energy for buildings. The effects of global warming on reducing building heating energy demand should be considered in future climate projections.

This study provides valuable insights into how the energy-saving effectiveness of cool roofs and green roofs can be influenced by the specific characteristics of the local ambient climate and urban context. This information can be used to inform the selection and design of appropriate roof mitigation strategies in different urban areas, helping them adapt to and mitigate the impact of future climate change.