关键词: 通风廊道, 城市化, 地表粗糙度, 城市热岛, 数值模拟, 北京市, 土地利用, 土地覆盖

Abstract:

From the perspective of local and micro scales, construction of ventilation corridor in urban area was proposed by optimized planning and architectural design in previous studies. However, for contemporary megacities and urban agglomerations, both urban heat island and pollutant transport may involve a larger scale of regional impact. It may have more practical significance to integrate regional natural geographical resources to identify and plan ventilation corridors in urban peripheral areas to be developed. Taking Beijing as an example, potential ventilating areas is preliminarily identified by drawing the map of aerodynamic roughness length in this study. First, monthly mean wind fields from numerical simulation outputs of January and July demonstrate that, in winter with strong background wind, the distribution of horizontal wind speed is highly consistent with the distribution of underlying surface roughness. There is an obvious wind path in the northeast of urban Beijing. Wind speed drop significantly when passing through the urban area due to the high surface roughness, and partially recoveries in the urban downstream. Second, thermodynamic analysis suggests that the low temperature area outside the city in summer is contrary to prevailing wind direction; both the size of the compensation space and thermal gradient between the compensation and the action space are smaller than that in winter, hence the available wind resources to refresh the city are scarce. Third, a dimensionless ventilation index is estimated by integrating the weighted surface temperature and roughness length. In Beijing, the index is in between 0 and 0.25 in winter, and is in between 0 and 0.60 in summer. The smaller the value is, the stronger the ventilation capacity. The ventilation capacity in winter is significantly better than that in summer due to the effect of seasonal thermodynamic difference. Fourth, the simulated velocity is further combined to divide the ventilation performances into 4 grades, and the potential ventilation corridors in Beijing are identified in winter and summer, respectively. In winter, the length of the ventilation corridor running through Beijing is about 200 km; it introduces wind resources from the periphery of the city to improve the self-purification capacity of the city. In summer when the background wind is weak, the connectivity of the wind path is poor and the ventilating capacity is weak. Optimizing urban agglomeration planning will be hence practical helpful.

Key words: ventilation corridor, urbanization, surface roughness, urban heat island, numerical simulation, Beijing, land use, land cover