Enhancing Urban Thermal Environment and Energy Sustainability With Temperature-Adaptive Radiative Roofs

Urban overheating presents significant challenges to public health and energy sustainability. Conventional radiative cooling strategies, such as cool roofs with high albedo, lead to undesired winter cooling and increased space heating demand for cities with cold winters, a phenomenon known as heating energy penalty. A novel roof coating with high albedo and temperature-adaptive emissivity (TAE)-low emissivity during cold conditions and high emissivity during hot conditions-has the potential to mitigate winter heating energy penalty. In this study, we implement this roof coating in a global climate model to evaluate its impact on air temperature and building energy demand for space heating and cooling in global cities. Adopting roofs with TAE increases global urban air temperature by up to +0.54 degrees C in the winter (99th percentile; mean change +0.16 degrees C) but has negligible effects on summer urban air temperature (mean change +0.05 degrees C). Combining TAE with high albedo effectively provides summer cooling and does not increase building energy demand in the winter, particularly for mid-latitude cities. Sensitivities of air temperature to changes in emissivity and albedo are associated with local "apparent" net longwave radiation and incoming solar radiation, respectively. We propose a simple parameterization of air temperature responses to emissivity and albedo to facilitate the development of city-specific radiative mitigation strategies. This study emphasizes the necessity of developing mitigation approaches specific to local cloudiness.