A comparative study of the influences of park physical factors on summer outdoor thermal environment, a pilot study of Mianyang, China

Along with global climate change and urbanisation, the thermal environment is increasingly worse in summer, especially (sub)tropical regions. In recent decades, approaches improving the thermal environment have been frequently investigated. Factors of urban design, planning, and landscaping have been found thermal relevant. These factors were indicated by sky view factor (SVF), vegetation cover, leaf area index (LAI) etc. However, most studies focused one single factor, thermal performance difference between various factors were rarely explored. This study compared park canopy closure (PCC) and LAI about their effects on park thermal comfort indicated by various indices (air temperature, Ta; mean radiant temperature, MRT; and physiological equivalent temperature, PET). The PCC was different from LAI by leaf layer quantity (overlapping). Through a field measurement conducting in 8 parks around Mianyang (a subtropical riverside city, China; summer of 2018). The results revealed, both PCC and LAI were significantly thermal effective, LAI showed less significant thermal effects than PCC in linear models. That is to say, leaf layers had little effect linearly. The effects of PCC on the various indices varied for daily periods, with a significant effect on MRT during the day, Ta in the evening, and PET throughout the day. Increasing PCC from 0 to 1 could reduce PET by 29.44 °C (afternoon, R2 = 0.4928). Findings of this study confirmed the different environmental factors’ impacts on microclimates and distinguished the characteristics of various thermal indices.