Modelling the efficiency of Nature-based Solutions to decrease extreme heat in dense urban areas in Vienna at micro- to city-scale

Urban environments experience high temperatures during heat waves due to their prevalence of built infrastructure and lack of unsealed, natural areas. This study analyses the effectiveness of Nature-based Solutions (NbS) to reduce urban heat in a densely built environment using a modelling approach that (i) represents realistic NbS implementation on a micro-scale and (ii) upscales their application for the entire city. The modelling approach is applied to the city of Vienna, Austria for a representative clear-sky hot day. The city-scale simulations are further combined with climatological data to evaluate the change in heat-related climate indices due to implementation of NbS and technical measures. A selected densely built area is simulated with the micro-scale ENVI-met model and an estimated NbS distribution/size is used as a base for city-scale simulations with the MUKLIMO_3 model. The city-scale simulations analysed in six separate scenarios show the greatest cooling effect for a combination of measures. Furthermore, the micro-scale model shows that NbS display a stronger cooling effect than the technical ones. The comparison of model simulations shows a similar cooling effect. Our results demonstrate that combined micro- and city-scale models can provide further insights into urban heat assessment and the impact of adaptation measures.