Impacts of Urban Form on Thermal Environment Near the Surface Region at Pedestrian Height: A Case Study Based on High-Density Built-Up Areas of Nanjing City in China

Abstract

The continuous worsening of urban thermal environments poses a severe threat to human health and is among the main problems associated with urban climate change and sustainable development. This issue is particularly severe in high-density built-up areas. Existing studies on the thermal environments (temperature data extracted from satellite remote sensing images) are mainly focused on urban canopy areas (airspace below the average height of trees or buildings) rather than the near surface region (at pedestrian height). However, the main outdoor activity space of urban residents is the area near surface region. Hence, this study aims to investigate the influence of urban form (i.e., building density, height, and openness) on thermal environment near the surface region. The high-density built-up areas of a typical megacity (i.e., Nanjing) in China were selected, and the thermal environments of 26 typical blocks were simulated using ENVI-met software. Temperature field measurements were carried out for simulation validation. On this basis, a classified and comparative study was conducted by selecting the key spatial form elements that affect thermal environments. The results showed that in actual high-density built-up areas, single urban form parameter does not determine the thermal environments near the urban surface but mainly affected by the use (function) of space. For this study, the overall thermal environment of a street block is optimal when the building density is between 40% and 50% and the average building height is between 8 and 17 stories. Nonetheless, the urban form can be improved to optimize the overall effects on building functions and thermal environments. Furthermore, function-specific urban form optimization strategies were proposed to optimize thermal environments according to specific functional needs.

Optimization Strategy of Traditional Block Form Based on Field Investigation—A Case Study of Xi’an Baxian’an, China

“…In the current study, the HF increased by 41.7, which reduced the average air temperature by 0.92 • C in the block. Yang et al showed that there is no direct correlationship between the air temperature and BD [42], which is similar to the results presented in the current paper. In addition, in a study of Hong Kong City, Cheung et al showed that the air temperature can be increased by 0.849 • C [54] by increasing SVF from 0 to 1.…”

“…The thermal environment and wind environment of six typical residential blocks in summer and winter solstice were simulated, and the air temperature and wind speed ratio of 6 monitoring points at the 1.5 m pedestrian level of each plot were analyzed during the period of 8:00-18:00. Combining the research scheme of Nanjing Xinjiekou and the investigation of Xi'an block morphology, we carried out the simulation study of idealized parameters as discussed in Section 2.3 [6,42]. BD refers to the proportion (%) of the total base area of buildings and the occupied land area within a certain range.…”

Temperature Reduction Effects of Rooftop Garden Arrangements: A Case Study of Seoul National University

“…When the ratio of increasing green area was fixed at 60%, there was a temperature reduction effect of at least −0.44 • C, up to −2.0 • C, depending on the installation rate of the permeable pavement. The last prior research identifies the effect of urban form and specific building functions on the thermal environment [12]. This study suggests that the optimal size, height, and layout of buildings were presented in different ways.…”

Convivial Greenstreets: A Concept for Climate-Responsive Urban Design

“…The adaptation of urban areas to climate change is most challenging in compact areas, where changes to the urban form (e.g., street orientation, built density, average heights, built heritage, infrastructure) are difficult, at least compared to newly built areas [3]. While it is known that the urban form directly impacts urban microclimates [48], it is not likely that an entire block or a building listed as heritage will be demolished to improve, say, wind flow in an outdoor space. It follows that newly built forms are just the tip of the iceberg and that a more sustainable built environment calls for action upon existing buildings and infrastructures (and spaces) [49].…”