Modelling the potential of green and blue infrastructure to reduce urban heat load in the city of Vienna

The climate warming trend and city growth contribute to the generation of excessive heat in urban areas. This could be reduced by introducing vegetation and open water surfaces in urban design. This study evaluates the cooling efficiency of green and blue infrastructure to reduce urban heat load using a set of idealized case simulations and a real city model application for Vienna. The idealized case simulations show that the cooling effect of green and blue infrastructure is dependent on the building type, time of the day and in case of blue infrastructure, the water temperature. The temperature reduction and the size of the cooled surface are largest in densely built-up environments. The real case simulations for Vienna, which include the terrain, inhomogeneous land use distribution and observed climate data, show that urban planning measures should be applied extensively in order to gain substantial cooling on the city scale. The best efficiency can be reached by targeted implementation of minor but combined measures such as a decrease in building density of 10 %, a decrease in pavement by 20 % and an enlargement in green or water spaces by 20 %. Additionally, the modelling results show that equal heat load mitigation measures may have different efficiency dependent on location in the city due to the prevailing meteorological conditions and land use characteristics in the neighbouring environment.