Spatiotemporal Linkage and Transmission of Canopy Urban Heat Islands in the Yangtze River Delta Urban Agglomeration: The Role of Heat Advection

The Canopy Urban Heat Island (CUHI) effect profoundly influences the urban thermal environments. While surface energy balance analysis provides a theoretical framework for diagnosing CUHI drivers, the non-local contributions of horizontal thermal transport, particularly Urban Heat Advection (UHA), remain insufficiently characterized. Utilizing five years of high-density meteorological observations and datasets from the Yangtze River Delta urban agglomeration in China, combined with high-resolution Weather Research and Forecasting (WRF) simulations, this study investigates the spatiotemporal linkages and thermal transport mechanisms of regional CUHI under the influence of UHA. The results show significant spatial divergence under prevailing wind conditions: upstream cities experience CUHI attenuation through enhanced ventilation, whereas downstream cities exhibit intensified thermal loads via advective heat. UHA displays distinct diurnal asymmetry, typically stronger at night than during the day, with its peak mean intensity reaching approximately 0.6°C. UHA magnitude is non-linearly regulated by the wind speed and boundary layer turbulence mixing; it modulates downstream CUHI through two pathways: canopy horizontal heat transport, and the long-range transport and vertical mixing of urban boundary layer plumes. These findings deliver important insights for understanding the coordinated evolution of regional-scale CUHI within urban agglomerations.