The modulation of synoptic weather patterns and human activities on the diurnal cycle of the summertime canopy urban heat island in the Yangtze River Delta Urban Agglomeration, China

Synoptic weather patterns (SWPs) and human activities are significant driving factors of the canopy urban heat island effect (CUHI), and the CUHI phenomenon exhibits a pronounced diurnal cycle. However, to date, there has been a significant knowledge gap in understanding how the combination of SWPs and human activities modulates the diurnal cycle of CUHI. This study systematically analyzed the diurnal patterns of CUHI intensity (CUHII) in the Yangtze River Delta Urban Agglomeration (YRDUA) by integrating multiple source datasets and utilizing objective classification methods. Among all SWPs, type 2 (dominated by subtropical high pressure) exhibited the strongest CUHII, while type 4 (affected by southwestern moisture and southward cold air) had the lowest. In terms of human activities, landscape percentage (PLAND), largest patch index (LPI), and anthropogenic heat flux (AHF) showed an increasing trend, with higher values in the east and lower values in the west, coinciding with the spatiotemporal patterns of CUHII. These findings collectively confirm the pivotal roles of SWPs and human activities in CUHI phenomena