Spatiotemporal impact of vehicle heat on urban thermal environment : a case study in Hong Kong

Abstract

Vehicle heat (VH) is a substantial portion of anthropogenic heat and can affect the urban thermal environment. Quantifying the impact of VH has implications for the potential benefits of electric vehicles in cities, yet the spatiotemporal impact of VH has not been investigated separately. This study incorporates VH and urban landscape data into the Weather Research and Forecasting (WRF) model to estimate the VH impacts at a fine spatial resolution over Hong Kong. Results show a strong temporal variation of the VH impact at daily, weekly, and seasonal scales: 1) the warmth of urban canyon air temperature is stronger and more consistent at night than in daytime, 2) increases in sensible heat fluxes are more pronounced during weekdays than weekends, 3) temperature change of 0.35 °C in winter is larger than that of 0.32 °C in summer. Increased air temperature over the land area by VH correlates with urban area fraction and building height positively, but not the aspect ratio. The statistically significant VH impact (90% confidence level) has the broadest spatial coverage in Hong Kong shortly after rush hours. The relative VH impact compared to building heat demonstrates the dominative role of vehicle heat in warming low urbanized areas with highways and circulation roads. The spatiotemporal distributions of the VH impact provide insights into the potential benefits of green transportation technology and policy in mitigating urban heat islands.