The Impact of Changes in Green Space Structures on Thermal Mitigation and Costs under a Constant Green Volume

Green space improves outdoor thermal comfort and promotes the residents’ physical and mental health. Currently, many cities are using green volume indicators to evaluate the quality of residential green space and to help form the latest evaluation standards. However, from the perspective of plant green volume, the impact of green space structures on thermal mitigation has not been emphasized. Furthermore, the cost of green space will change with the green space structures. Therefore, we evaluate the impact of changes in green space structures on thermal mitigation and costs from the perspective of plant green volume and aim to find suitable allocations of plant green volume, which balance thermal mitigation with cost savings. This study analyzed the regional climate and residential green space structures. Then, we discussed the relationship between thermal mitigation and the costs of different structures. The analytical results indicated that thermal comfort improves as the green volume of trees increases, with costs also increasing. Where the green volume exceeds 70%, no “extreme heat stress” moments occur for the whole day. When the green volume of trees increases from 20% to 60%, the thermal mitigation is 3.62 °C. However, the mitigation is only 1.74 °C when the green volume increases from 60% to 100%, which is less than half of the former, numerically. This study suggests that the green volume of trees in residential green spaces should be controlled at 60%–70% and the corresponding green volume of shrubs should be 30%–40%. This study rationally balances the thermal mitigation and costs of residential green space, which will directly guide residential green space planning in real situations.