A review on the significance and perspective of the numerical simulations of outdoor thermal environment

• Compare existing numerical simulation models and thermal indices. • Evaluate model validation of different meteorological variables and thermal indices. • More studies are required for Southern Hemisphere and winter conditions. • Combining survey and simulation results can optimize mitigation strategies. • Multi-scale modelling is required to examine climate change impact on microclimate. Computer simulation programs have been used since 2006 for analyzing outdoor human thermal environments. This study reviewed 130 peer-reviewed papers published during 2006–2019, which investigated outdoor thermal comfort using computer simulations. Most studies were conducted in the Northern Hemisphere and the temperate oceanic climate during summer. The widely used computer simulation program and thermal indices were the ENVI-met and physiological equivalent temperature, respectively. To validate the simulation results for urban planning and design, 61 % of the studies compared the simulation results with observation data. Moreover, 45 % and 27 % of the studies validated the simulation results with measured air temperature and mean radiant temperature, respectively. Thermal indices were validated in 12 studies. Mitigation strategies to improve urban outdoor thermal environments can be analyzed in three categories: the effects of urban geometry, urban vegetation, and surface materials. To address the impact of climate change, future studies should consider the future urban structural plan and design scenarios, such as building heights, street orientations, and surface types. Moreover, further studies can adopt multi-scale approaches (e.g. global scale, mesoscale, and micro-scale). This study will help researchers select a suitable numerical simulation program according to their requirements.