Abstract
Numerous cities face the serious problems of rapid urbanization and climate change, especially in recent years. Among all cities, Wuhan is one of the most affected by these changes, accompanied by the transformation of water surfaces into urban lands and the decline of natural ventilation. This study investigated the impact of surface urban heat island enlargement (SUHI) and block morphology changes in heat balance. Accordingly, the interactive impact of building diversity with major building forms (low-rise, mid-rise, and high-rise) on thermal balance and microclimate changes under the influence of urban land expansion at the residential block scale was studied. To investigate the heat balance changes by air temperature intensification and air movement reduction, a long-term and field observational analysis (1980–2018) coupled with computational fluid dynamic simulation (CFD) was used to evaluate the impact of building diversity on thermal balance. Outcomes show that urban heat island intensity (UHII) increased by 2 °C when water surfaces in urban areas decreased; consequently, there was a deterioration in the air movement to alleviate UHII. Thus, the air movement declined substantially with UHII and SUHI enlargement, which, through increased urban surfaces and roughness length, will become worse by 2020. Furthermore, the decline in air movement caused by the transformation of urban water bodies cannot contribute to the heat balance unless reinforced by the morphology of the urban blocks. In the design of inner-city blocks, morphological indicators have a significant impact on microclimate and heat balance, where increasing building density and plot ratio will increase UHII, and increasing water surfaces will result in an increase in urban ventilation. Lastly, a substantial correlation between air temperature and relative humidity was found, which, together with the block indicators, can help control the air temperature and adjust the urban microclimate.
Highlights
Urbanization is a global phenomenon resulting in urban expansion, land use/cover transformation, and climate change [1,2]
In the design of inner-city blocks, morphological indicators have a significant impact on microclimate and heat balance, where increasing building density and plot ratio will increase urban heat island intensity (UHII), and increasing water surfaces will result in an increase in urban ventilation
(e) Overall, building density is the most important morphological indicator to increase UHII compared with open spaces which, according to the plot ratio indicator, can reinforce air movement and increase natural ventilation to mitigate the negative effects of UHIIs
Summary
Urbanization is a global phenomenon resulting in urban expansion, land use/cover transformation, and climate change [1,2]. As a result of urban sprawl, urban morphology has significantly changed and urban surfaces have become geometrically complex, dense, and highly diverse with higher thermal capacity and more impervious surfaces compared to rural surfaces [6] In this regard, natural elements/surfaces have been transformed by the use of manufactured materials with distinctive thermal and radiative properties, which has caused surface urban heat island (SUHI) enlargement. Natural elements/surfaces have been transformed by the use of manufactured materials with distinctive thermal and radiative properties, which has caused surface urban heat island (SUHI) enlargement These properties create multiple reflections among buildings through long-wave (LW) and short-wave (SW) radiation, which can considerably impact on thermal balance. Urban form causes the formation of various microclimates within the built environment [6]
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