Observational and modeling study of interactions between urban heat island and heatwave in Beijing.

Heatwaves have considerable socioeconomic impact. Because of the urban heat island effect, risks associated with heatwaves are exacerbated in urban areas compared with surrounding regions. This study investigated the behaviors of local-scale urban heat island during a heatwave in Beijing using in situ observations and kilometer-scale simulations based on the Weather Research and Forecasting model. Results showed the observed urban heat island was enhanced by 0.78 °C during the heatwave episode, with greater increase at night than during daytime. The model with gridded urban canopy parameters was able to capture the spatiotemporal variation of surface air temperature, although it overestimated the magnitude. Spatial variation of urban canopy parameters could improve simulation of the spatiotemporal variations of near-surface air temperature in urban areas. Using a biophysical factorization method, urbanization-induced temperature changes were attributed to different driving factors. Results suggested that heatwave-related enhancement of urban heat island during daytime is primarily because of increased urban–rural contrast in surface evapotranspiration, whereas such enhancement at night is associated mainly with greater anthropogenic heat and enhanced warm advection. Since climate change make heatwaves more frequent, intense and persistent, targeted implementation of adaptation measures are needed to reduce the negative effects of urban heat island and to minimize their related risks to public health, power grids, and infrastructure. • This paper demonstrates the enhancement of urban heat island (UHI) due to heat wave using observations and numerical model. • Observed UHI in Beijing was enhanced by 0.78 °C during a heatwave episode, more profoundly during night than during daytime. • Enhanced UHI is due to increased urban–rural contrasts in surface evapotranspiration, anthropogenic heat and warm advection. • Synergistic interactions between UHI and heatwave present further heat-related risks for urban society and residents. [ABSTRACT FROM AUTHOR]