For the mitigation of urban heat island and urban noise island: Two simultaneous sides of urban discomfort

Urban environment well-being has become a crucial public issue to face, given the huge concentration of population and climate change-related hazards at a city scale. In this view, Urban Heat Island (UHI) is now very well-acknowledged to be able to produce a serious threat to populations around the world and compromise human well-being due to aggressive overheating, exacerbated by anthropogenic actions. The same anthropogenic actions are also responsible for other discomfort causes such as noise pollution, which has also been demonstrated to heavily impact societal life and health conditions in urban systems. Both these phenomena typically co-exist in terms of space and time coincidence, and they both may be mitigated by means of smart adaptive and multifunctional surfaces including urban pavements and building envelopes. This review bridges the gap between only-thermophysical analysis about UHI mitigation and only-acoustics analysis of urban noise pollution, here defined as Urban Noise Island (UNI). To this aim, the key physics background of mitigation techniques is presented and the most innovative and promising solutions for counteracting UHI and UNI are described, with the final purpose to foster research and innovation towards more livable cities through a multiphysics and holistic view.