Pitfalls and Potentials of Microclimate Simulations in Urban Planning

In the face of climate change and rising mean global temperature, urban planning is required to transform cities into resilient living areas for present and future generations. Within this task, microclimate simulation models are an important tool to assess the impact of nature-based solutions (NBSs), building morphology, design of urban quarters, and other measures on the local microclimate. As simulation tools are open to be applied by different user groups, the utilization of the software is often kept as easy as possible. This seeming simplicity bears the risk for users to fall into traps during the model configuration, interpretation of results, or not making use of the full potential of simulations. While scientific literature mainly describes successful application of case studies, it does not cover potential misapplication and related consequences. The present study contributes to closing this research gap and supports the urban planning community with a selection of pitfalls in the model setup and interpretation of results. Clear examples of wrong configuration of wind direction, inaccurate evaluation of mean radiant temperature (MRT), and improper selection of performance indicators are presented by the means of sensitivity experiments and case studies with the modeling software ENVI-Met. The prevailing study demonstrates why MRT values are not suitable to explain effects of NBS during nighttime and contrasts the effects of façade greening on air temperature (0.85°C) with building surface temperature (6.1°C or even 27.5°C with substrate layer). In addition, it highlights the potentials of the multitude of possible performance indicators of microclimate simulations. The selection of avoidable mistakes in the assessment of the local microclimate supports users of microclimate models to promote effective and impactful climate adaption and mitigation measures in urban planning.