Effects of orientation of urban roads on the local thermal environment in Guangzhou City

Abstract

The continuous Guangzhou expansion leads to more and more construction of the city road, which is a special underlying surface. In 2012, the total length of the road in Guangzhou is 9050.715 km. Among them, the total length of the highway is 652.6 km and the remaining 6044 km is urban roads. There are 47 main roads with a distance of 5685 km and area of 3953.63 million square meters. The roads are commonly constructed by asphalt and cement concrete whose heat absorption rate is higher than that of the green land and water body, while the thermal capacity of the asphalt and cement concrete is smaller than that of the green land and water body. This means that the roads with asphalt and cement concrete can absorb the solar radiation largely and cause the big temperature increase itself, which will increase the summer energy consumption of vehicles on the road and affect the outdoor thermal comfort of pedestrians. Nowadays, the construction of roads has become one of the main-reasons for urban heat island. In another hand, road provides the broad path for urban ventilation, which makes it become an important element for the construction of urban wind corridor. According to above negative impact on urban heat island and positive impact on urban ventilation, great difficulties still remain when urban planners attempt to design the urban roads to realize the comfortable outdoor thermal environment. The orientation of urban roads is an important element for the road design. Its relationship with the prevailing wind direction can somehow affect the city temperature distribution and ventilation efficiency. Fazia Ali-Toudert from University of Freiburg concludes that in urban street the roads with east-west orientation are less efficient in releasing heat compared with the north-south orientation (Fazia Ali-Toudert, 2006). Andreou concludes that, under the same condition of shade and solar energy, street geometry, height/width ratio, orientation and trees can affect urban canyon microclimate (Fazia Ali-Toudert, 2014). They do not have a detailed study of the relationship between the orientation towards the prevailing wind, as well as to the impact on the surrounding thermal environment This paper uses the method of numerical simulation to analyze the impact of road orientation on the thermal environment of Guangzhou Zhujiang New Town. Some implications for the urban road design are obtained. Orientation of the road has a great influence on the local thermal environment for example in windless area or with respect to high-rise buildings in low-lying areas.