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.
Highlights
Urbanization provides a high quality of urban life, and causes various environmental problems, which have received increasing attention in society [3]
The study results showed that the urban form could affect the thermal environments of street blocks
According to the analysis of XCZ in Nanjing, the specific street block morphology is closely related to the thermal environment, and the thermal environment varies with the street block morphology
Summary
Urbanization provides a high quality of urban life, and causes various environmental problems (e.g., climate change [1,2]), which have received increasing attention in society [3]. The surface material of green open space disturbs solar radiation and its transpiration, thereby increasing the air humidity, promoting air circulation, and reducing heat-island circulation inside high-density built-up areas [20]. The most existing studies on thermal environments (reflecting the characteristics of urban canopy layer), are based on air temperature data acquired via fixed-point meteorological observations and satellite remote sensing imaging by automatic meteorological stations in the professional observational networks operated by weather bureaus [25,26,27,28,29] It was asserted that measured data can directly reflect the effects of various factors but do not affect the relationship between the urban form and thermal environment
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