Potential role of local contributions to record-breaking high-temperature event in Xiamen, China

A record-breaking extreme high-temperature (EHT) event of 39.6 °C occurred in the coastal city of Xiamen, China, on August 9, 2019. The unique weather background and topographical features of Xiamen resulted in this event. In this study, the Weather Research and Forecast model with urban land use and landscape data, obtained using the local climate zone classification method, was used to simulate the aforementioned EHT event. The simulation results based on the refined underlying surface accurately reproduced the temporal and spatial distributions of the meteorological elements to enable investigation of the local contributions to air temperature during the EHT event. Tall buildings weakened the cooling effects of convective motions; thus, the intensity of the urban heat island (UHI) still reached 2.8 °C under strong background wind conditions as geostrophic wind speeds exceeded 10 m s−1. The northwest wind not only generated a foehn wind, which caused the urban area close to the mountain to directly heat up by about 2 °C, but also prevented the southeasterly sea breeze from delivering a cold and humid air mass. Thus, a high temperature was maintained in urban areas. Such local contributions from background wind and the weakening of surface winds by urban buildings are key reasons for this EHT event. Past EHT events also exhibit similar local characteristics. In summary, our results are informative for the prediction of future EHT events in Xiamen and other cities with similar topographical features when similar circulation patterns occur.