A Study on the Effect of Green Plot Ratio (GPR) on Urban Heat Island Intensity and Outdoor Thermal Comfort in Residential Areas

Greenery impacts the urban thermal environment, but the benefits of the three-dimensional green volume of space have not been effectively evaluated. In this paper, we analyzed the impact of 3D greenery on urban heat island intensity and thermal comfort in residential areas from the perspective of the green plot ratio (GPR). We selected a typical residential area, set up simulation models, and then analyzed the effect of different GPR values on the outdoor thermal environment using the validated ENVI-MET simulation. The results showed that increasing GPR in residential areas can effectively reduce the intensity of urban heat island and improve thermal comfort. When the GPR reaches 0.5 and 1.5, the thermal comfort level of the building overhead space and the north-south street space decreases from "very strong thermal stress" to "strong thermal stress". When the GPR reaches 2.5, the outdoor thermal comfort of the east-west street space and courtyard space is reduced to "hot". When the GPR is higher than 0.5, the urban heat island intensity in the north-south street space decreases by one level, from "very strong" to "strong". When the GPR reaches 3.5, all four types of spaces have "moderate" urban heat island intensity. Increased GPR exacerbates urban heat island intensity to some extent and worsens outdoor thermal comfort due to the nocturnal insulating effect of plants. Based on the results, the study proposes the bottom-line control of the GPR index from the perspective of urban heat island mitigation and thermal comfort improvement. This paper points out the benefits of GPR in residential areas in improving the human environment, which is of great practical value for developing urban residential environment from "increasing quantity" to "improving quality".