Interaction among local flows, UHI, coastal winds, and complex terrain: Effect on urban-scale temperature and building energy consumption during heatwaves

Abstract

Extreme heat aggravates thermal stress and electricity shortage in urban areas. This study investigates the (circulating) winds in Hong Kong during a heatwave. Unprecedentedly, the collective effect of coastal winds, complex terrain, and local flows on urban temperatures and air-conditioning load intensity (ACLI) is examined using the mesoscale Weather Research and Forecasting (WRF) model. Three representative wind patterns, including urban-accelerated channel wind, channel-wind-induced heat advection, and urban-mountain-stagnated sea-breeze, are analyzed. Our results show that the mountain blockage in foothill areas would increase 2-m temperatures (T2) and ACLI by 1 °C to 2 °C and 5 W/m2, respectively. ACLI in compact high-rise areas (LCZ 1) is most sensitive to extreme heat. Moreover, the urban heat island (UHI) downstream is crucial that would accelerate channel flows by 1.66 m/sec (50.26 %). On the other hand, terrain-induced channel winds augment heat advection, increasing downstream T2 (0.7 °C) and ACLI (2.62 W/m2). UHI-induced local flows interact with hilly slopes, stagnating the sea breeze on mountain leeward side. Subsequently, the winds would be slowed down by 0.81 m/sec while the temperature T2 would be increased by 0.9 °C in downstream urban areas. Eventually, the daytime ACLI could be raised as much as 6.41 W/m2.