Weekly rhythms of urban heat islands: A multicity perspective

Abstract

Investigating the weekly rhythms of urban heat islands (UHIs) is critical for gaining deep insights into the urban climate changes caused by periodic cycles of human activities. However, the weekly rhythms of both canopy and surface UHIs (termed Ic and Is) remain poorly understood at a large spatial scale. Leveraging daily screen-level air temperature (Ta) and satellite land surface temperature (Ts) observations (2015∼2020), we show that the weekly rhythms of Ic averaged for all selected cities exhibit an evident peak-and-valley pattern across most seasons, with the annual mean Ic reduction during weekends of 0.09 ± 0.01 K (mean ± S.E., p < 0.05) for daytime and 0.10 ± 0.01 K (p < 0.05) for nighttime when compared to weekdays. In contrast, the Is only displays a pronounced weekly rhythm during winter daytime, with the corresponding Is reduction during weekends of 0.07 ± 0.01 K (p < 0.05) relative to weekdays. These findings remain robust against potential observation errors in Ta and Ts. From an intra-city perspective, both Ic and Is reductions during weekends escalate with increasing urban impervious surface percentage. This study illustrates the significance of short-term cycles of human activities in shaping global urban climates.