Strong Modulation of Human-Activity-Induced Weekend Effect in Urban Heat Island by Surface Morphology and Weather Conditions

The weekend effect of the canopy urban heat island (UHI) has been long recognized. However, how the UHI weekend effect (UWE) varies with the hour of day and season of year is still unclear; it remains largely unknown on how the UWE is regulated by various controls. To address these knowledge gaps, here we took Beijing, China as an example and investigated the detailed spatiotemporal UWE patterns and the major regulators with a 3-year data set of in-situ surface air temperatures. Our results indicate that the annual Delta I-c (the UHI intensity difference on weekends and weekdays) is stronger at night (-0.13 +/- 0.12 K; mean +/- 1 STD) than during the day (-0.05 +/- 0.10 K); at the seasonal scale, Delta I-c reaches the strongest in winter (-0.14 K) and the weakest in summer (-0.05 K). The Delta I-c is strongly regulated by anthropogenic heat flux (AHF), evidenced by a quasi-synchronous diurnal pattern between Delta I-c and Delta HF (i.e., the AHF difference between weekends and weekdays). The nighttime Delta I-c is intensely modulated by urban morphology, with a stronger modulation by the landscape shape index than by the distance of the station from the urban center. Weather conditions also modulate the Delta I-c, with the Delta I-c weakening with the increase of cloud coverage and wind speed level. We consider these findings deepen our understanding of the weekly rhythms of UHI as well as the underlying modulators.