Practical guidelines to resilient urban planning against outdoor heat stress

In urban areas, dense building geometry and limited tree canopy cover causes an increased risk of heat stress on the urban population, especially during heatwaves. As cities grow larger and denser, these variables are important to consider in urban planning. The challenge that urban planners face is knowing which mitigation that is most efficient in achieving the highest cooling effect. It is therefore necessary to quantify the effect of different building geometries and tree canopy cover on outdoor heat stress in dense urban areas, to provide a knowledge base for urban planners, developers and authorities. The aim of this study is to develop guidelines based on the quantified effect of different building geometries and tree canopy coverage on outdoor heat stress, which may be used into urban planning. Microscale modelling was used to evaluate the local influence on the thermal comfort index Physiological Equivalent Temperature (PET), with respect to building geometry and tree cover. Six different building geometries and two variations of tree canopy cover of 5 % and 15 % respectively, were investigated. PET calculations were conducted with high resolution spatial data of mean radiant temperature (T_mrt) and wind speed. T_mrt were calculated using the SOLWEIG (SOlar and LongWave Environmental Irradiance Geometry) model within the Urban Multi-scale Environmental Predictor (UMEP) tool, whereas wind speed was calculated using the Computational Fluid Dynamics (CFD) model MISKAM (microscale climate and dispersion model). Preliminary results show that a building geometry of high-rise apartments result in a higher outdoor heat stress in relation to a building geometry with closed courtyards. Initial results of tree canopy cover, for closed court yards, only show a minor reduction in outdoor heat stress with a 5 % tree canopy cover, whereas 15 % tree cover highly reduced the heat stress risk in courtyards and adjacent streets.