Cooling effect of the pocket park in the built-up block of a city: a case study in Xi'an, China.

Pocket parks, the green infrastructures with small sizes and flexible layouts, are suitable for thermal environment improvement in the urban built-up block with limited green space. To quantify the relationship between pocket parks and the thermal environment in western China, two parks in the built-up block of Xi'an were selected. By field measurement, the cooling effect could be extended 100 m from the park boundary, connecting two parks. Furthermore, the road and greening within the block demonstrate significant influence on the cooling diffusion by regression analysis. Based on ENVI-met simulation, the ratio of the tree and the grass, the layout of the tree and the grass, and the layout of the paving were analyzed at different proportions of greening and paving of the park. Finally, a combination of the daytime physiological equivalent temperature (PET) and nighttime air temperature (AT) was proposed to choose the optimum layouts: the trees concentrated in the center and the pavement with more roads. Results can provide insights for designing pocket parks based on the thermal environment improvement.

The renew plans of urban thermal environment optimization for traditional districts in Xi'an, China.

During the process of the high-speed urbanization in Chinese cities, the social, economic, and political status and the interaction between each factor have been more focused on urban traditional district renewal. However, the effects on urban microclimate and the residential living conditions in traditional districts are not well discussed, which is strongly related to the living comfort and citizens' well-being. In this study, two typical traditional districts in Xi'an are selected. According to the original situation of building functions and the community characteristics, two renewal plans are proposed by adding vegetation in open spaces (V), and adding vegetation combined with building redevelopment (V&B), in order to balance the living convenience and thermal environment. Via ENVI-met simulation, the effects of the district renewal plans on thermal environment including wind speed, air temperature, and mean radiant temperature are evaluated. This study provides method of environmental evaluation for traditional district renewal, which contributes to sustainable urban planning in historical districts, and provides recommendations for related policy development.

Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates.

Growing and densifying cities set a challenge for preserving and enhancing green spaces to cool urban spaces. Green roofs, involving the planting of vegetation on rooftops, are regarded as an alternative approach to enhancing urban greenery and urban cooling. For better cooling performances, it is essential to reasonably configure green roofs, especially in real and complex neighborhoods. Therefore, the aim of this paper is to investigate the impact of morphological characteristics of green roofs on pedestrian cooling in real and complex neighborhoods. In specific, based on an ENVI-met model, we studied the effect of greening layout, coverage ratio, vegetation height, and building height on pedestrian air temperature reduction in the tropical city of Hangzhou, China. Results indicate green roofs could generate moderate effects on pedestrian air temperature reduction (around 0.10⁻0.30 °C), while achieving a cooling performance of 0.82 °C. Green roofs in upwind zones were able to generate the most favorable cooling performance, while green roofs in downwind zones made slight differences to pedestrian thermal environments. Green roofs with a low coverage ratio were not useful for lowering pedestrian temperature, and a greening coverage ratio of 25⁻75% in upwind zones was cost-effective in real neighborhoods. Locations that were horizontally close to green roofs enjoyed better cooling performances. Increasing vegetation height could strengthen cooling effects of green roofs, while an increase in building height weakened the cooling performance. Nevertheless, higher building height could enhance pedestrian cooling performances because of building shading effects. In addition, because of wind effects and building shading, building height limits for the cooling performance of green roofs could be higher than 60 m.