As an integral part of urban forests, urban parks play a vital role in mitigating urban heat islands (UHI) and providing residents with comfortable outdoor recreational plots. For high-quality use of the trees in regulating the thermal comfort of urban parks, previous studies primarily focused on the microclimate variations caused by tree coverage and morphological features separately. However, there is still a lack of systematic understanding of how tree canopy coverage (TCC) and its morphological elements, including leaf area index (LAI), trunk height (TH), and crown diameter (CD), combined affect the thermal comfort in the urban park. This study employed an orthogonal experiment design and ENVI-met software to simulate the microclimate of various multi-factor combination models in the case of a typical urban park in a temperate continental climate zone in China, analyzing the simulated result through physiological equivalent temperature (PET). Results show that the contribution ratio of various elements to the thermal environment vary over time. In studied elements, the contribution ratio of TCC to PET is consistently higher than 50% during the morning, midday, and evening periods, reaching a peak of 67% in the evening. The maximum contribution ratios for CD, TH, and LAI occur during midday, morning, and midday, respectively, with corresponding contribution ratios of approximately 22%, 10%, and 9%, respectively. The ranking of elements affecting thermal comfort in the urban park generally is TCC, CD, LAI, TH throughout the day, apart from the morning, when the influence of TH is greater than LAI. The optimal combination of elements is 85% TCC, 4m TH, 3.9 LAI, and 7m CD, and thirteen combinations of element cases meet the thermal comfort requirements during summer. The research findings highlight the significance of optimizing the configuration of trees in creating a more comfortable and inviting space for human activities.

A comfortable thermal environment in outdoor spaces is beneficial to people’s physical and mental health in cold conditions during winter. Greenery can improve outdoor thermal comfort (OTC) via microclimates in winter. Multiple methods have been employed to investigate how greenery influences OTC and microclimate. However, the underlying mechanism of how microclimate participates in the regulation of the effect of greenery on OTC is unclear. To examine the mediating effect of microclimate on the relation between greenery and OTC in cold weather during winter, we conducted meteorological measurement and thermal comfort surveys in Zhengzhou, a city in China’s cold region, from 29 to 30 December 2019. Two objective greening indices from different dimensions were extracted at twelve sampling points: (1) the green view index (GVI) from horizontal normal images from people’s perspective, and (2) the tree view factor (TVF) from vertical-upward fisheye images. With microclimatic parameters as the mediators, a comprehensive multi-step mediation analysis was conducted. The regression results revealed that the GVI and TVF were negatively associated with the thermal comfort vote (TCV) (i.e., the more greenery, the less TCV, which means the more comfortable the thermal environment). Our findings show that both GVI and TVF contribute to OTC through different mechanisms in cold climatic conditions during winter. Vegetation in sight revealed by the GVI can directly regulate OTC by affecting people’s mental feelings or other factors. Air temperature (Ta), relative humidity (RH), and wind speed (Va) served as significant partial mediators for the GVI. Moreover, there was a complete mediation for TVF–OTC correlation with Ta, RH, and Va as significant mediators. The mediating effects of microclimate accounted for 81.00% for GVI and 89.02% for TVF, respectively. The GVI is propitious to the study of people’s mental health and landscape preferences, whereas TVF is suitable for studies on microclimate adaptation.