A systematic review of the impact of green walls on urban comfort: temperature reduction and noise attenuation

Achieving sustainable urban development requires a reorientation in the planning, management, and design of cities based on the use of cross-cutting solutions that can systematically address urban problems. The implementation of Nature-based Solutions (NBS) such as green walls in cities contributes to reducing the effects of a systemic issue: climate change. This field of research is constantly evolving, and there is a growing need for systematic analysis to understand the current scenario, identify gaps, and accelerate new lines of research. This review aims to demonstrate the impact of green walls on urban comfort by providing a systematic review of the state of the art in the field of temperature reduction and acoustic absorption, identifying the factors that influence urban comfort through the use of vegetation, and highlighting research gaps that can be further explored. The most relevant results have shown that the temperature reduction is mainly influenced by the shading capacity of the selected vegetation type, the evapotranspiration process of the plants, and the presence of substrate. Also, the acoustic absorption capacity is influenced to a greater extent by the system's configuration, the substrate's characteristics, and the vegetation's density. In both cases, the environmental conditions in which they are found can vary the impact to a greater or lesser extent. The results of this research are relevant for the implementation of green walls as a climate change mitigation tool in cities and the development of new research approaches.