Urban heat mitigation assessment based on surface unsealing potential and microclimate modelling

Source abstract

Global climate change causes rising temperatures and more frequent heat waves in Central European cities. Combined with ongoing urban densification, this exacerbates the urban heat island (UHI) effect. Consequently, city residents are increasingly exposed to heat stress and related health risks. Climate change adaptation measures, such as unsealing impermeable surfaces, are required to reduce heat loads in the urban fabric. To our knowledge, the cooling performance of unsealing measures at the neighborhood scale - based on an assessment of potential areas suitable for unsealing - has not been previously analysed. To fill this research gap, we developed a mixed-method approach consisting of (a) a scoring framework to identify areas with unsealing potential, and (b) a sensor-validated microclimate model (ENVI-met) to simulate the cooling effects. Analyses were performed for two 16-hectare urban study areas in Cologne, Germany, both significantly affected by the UHI effect. Three model scenarios of low, medium, and high unsealing potential were simulated in each study area to investigate the heat mitigation performance compared to the status-quo. We found a statistically significant mean cooling effect of up to -1.28 K on for temperature at pedestrian height during a simulated 3-day heat event. The mean physiological equivalent temperature (PET) was reduced by up to -4.91 K. The findings highlight the effectivity of unsealing in the urban fabric and demonstrate the relevance of this combined assessment approach to support strategical decision making in urban planning.