School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, PR China 510275.
Department of Mechanical Engineering, the University of Hong Kong, Pokfulam Road, Hong Kong.
Sci Total Environ. 2020 Jul 15;726:138147. doi: 10.1016/j.scitotenv.2020.138147. Epub 2020 Mar 31.
Street aspect ratios and urban thermal storage largely determine the thermal environment in cities. By performing scaled outdoor measurements in summer of 2017 in Guangzhou, China, we investigate these impacts on spatial/temporal characteristics of urban thermal environment which are still unclear so far. Two types of street canyon models are investigated, i.e. the 'hollow' model resembling hollow concrete buildings and the 'sand' model consisting of buildings filled with sand attaining much greater thermal storage. For each model, three street aspect ratios (building height/street width, H/W = 1, 2, 3; H = 1.2 m) are considered. The diurnal variations of air-wall surface temperatures are observed and their characteristics are quantified for various cases. The daily average temperature and daily temperature range (DTR) of wall temperature vary significantly with different aspect ratios and thermal storage. During the daytime, wider street canyon (H/W = 1) with less shading area experiences higher temperature than narrower ones (H/W = 2, 3) as more solar radiation received by wall surfaces. At night, wider street canyon cools down quicker due to stronger upward longwave radiation and night ventilation. For hollow models, H/W = 1 attains DTR of 12.1 °C, which is 1.2 and 2.1 °C larger than that of H/W = 2, 3. Moreover, the sand models experience smaller DTR and a less changing rate of wall temperature than hollow models because larger thermal storage absorbs more heat in the daytime and releases more at night. DTR of hollow models with H/W = 1, 2, 3 is 4.5, 4.6 and 3.8 °C greater than sand models respectively. For both hollow and sand models, wider streets experience a little higher daily average temperature (0.3-0.6 °C) than narrower ones. Our study provides direct evidence in how man-made urban structures influence urban climate and also suggests the possibility to control outdoor thermal environment by optimize urban morphology and thermal storage.
街道纵横比和城市热储存量在很大程度上决定了城市的热环境。通过 2017 年夏季在中国广州进行的户外比例测量，我们研究了这些因素对城市热环境时空特征的影响，目前这些特征还不明确。我们研究了两种街道峡谷模型，即“空心”模型，类似于空心混凝土建筑，以及“沙”模型，由充满沙子的建筑物组成，具有更大的热储存量。对于每个模型，考虑了三种街道纵横比（建筑物高度/街道宽度，H/W=1、2、3；H=1.2m）。观察到空气-墙壁表面温度的日变化，并对各种情况下的特征进行了量化。墙壁温度的日平均温度和日温度范围（DTR）随不同的纵横比和热储存量而有很大差异。在白天，接收更多太阳辐射的较宽街道峡谷（H/W=1）比较窄的街道峡谷（H/W=2、3）经历更高的温度。在夜间，由于更强的向上长波辐射和夜间通风，较宽的街道峡谷冷却速度更快。对于空心模型，H/W=1 的 DTR 为 12.1°C，比 H/W=2、3 的 DTR 大 1.2°C 和 2.1°C。此外，由于热储存量较大，白天吸收更多热量，夜间释放更多热量，沙模型的 DTR 较小，墙壁温度变化率较小。空心模型的 DTR 分别比沙模型大 4.5°C、4.6°C 和 3.8°C。对于空心和沙模型，较宽的街道的日平均温度（0.3-0.6°C）略高于较窄的街道。我们的研究提供了人为城市结构如何影响城市气候的直接证据，并表明通过优化城市形态和热储存来控制室外热环境的可能性。
