Urbanization Magnified Nighttime Heat Waves in China

Abstract Nighttime heat waves have greater impacts on human society than daytime because nighttime heat waves deprive humans to recover from daytime heat and increase energy consumption for cooling. In this study, we found increased occurrence and severity of nighttime heat waves across China during 1980–2017 based on measurements from more than 2,000 meteorological stations. The nighttime heat waves have been longer lasting and occurred more often in spring and fall. Compared to rural areas, urban areas have shown enhanced frequency, intensity, and duration of nighttime heat waves. Urbanization accounted for nearly 50% of the extended duration and nearly 40% of the enhanced intensity and frequency of nighttime heat waves in urban areas relative to rural areas. Urban expansion, causing reduced evapotranspiration and weakened wind speed that normally cools the lower atmosphere by turbulent heat loss and cooled air advection, led to nighttime urban heat island, thus magnifying nighttime heat extremes.