The roles of meteorological parameters in Shanghai’s nocturnal urban heat island from 1979 to 2013

Urban heat island (UHI) represents important human-induced alterations in local climate that has extensive impacts on urban environments and the well-being of urban residents. Under the background of global warming and rapid urbanization, UHI effects will be greatly enhanced, which will further aggravate urban heatwaves and increase health risks to people therein. Therefore, to take adaptive mitigation measures, it is essential to thoroughly understand the meteorological mechanism responsible for the formation of UHIs. Here, we elucidate the roles of the main meteorological parameters in Shanghai’s nocturnal UHI intensity (UHII) using long-term meteorological data from 1979 to 2013. The strongest mean nocturnal UHII values were found in autumn and winter, whereas the weakest UHII was found in summer. This seasonal pattern was associated with dense cloudiness, high relative humidity and precipitation, strong winds, and low atmospheric pressure. Negative relationships between the nocturnal UHII and the cloudiness, wind speed, relative humidity, and precipitation and a positive correlation between the UHII and atmospheric pressure were observed for Shanghai. The interactive effects of the wind speed, cloudiness, and relative humidity on the UHII indicate that a calm, dry, and clear-sky environment was optimal for maximum UHI formation. This study provides insights into the mechanisms governing the formation of UHIs and clarifies the key meteorological factors. In addition, our results support the accurate assessment of future climate change impacts on human health and societies by including the UHII as an important assessment index.