Investigating urban wind vertical profiles during heatwaves with spatial synoptic classification using Doppler LiDAR: A case study in Hong Kong

Urban ventilation plays a critical role in mitigating heat risks, yet its behavior under extreme heat remains poorly understood, especially for high-density cities. This study integrates Doppler wind Light Detection and Ranging (LiDAR) observations with the Spatial Synoptic Classification (SSC) system to examine vertical wind speed profiles during heatwave (HW) periods from 2020 to 2024 across four sites in Hong Kong representing diverse urban and topographic conditions, ranging from open coastal environments to compact high-rise districts, reclaimed port islands, and suburban downwind areas. Results show significant wind speed reductions during HW periods, especially under dry tropical (DT) conditions. Moist tropical (MT) conditions, characterized by high humidity and cloud cover, show stronger wind shear than DT, especially in the lower 500 m. Comparisons with wind profiles from physical and numerical modelling reveal overestimation of wind speeds under extreme heat, resulting from their assumptions of neutral stratification or use of seasonal mean forcings. The findings indicate the limitations of conventional profiles in representing wind conditions under extreme heat. By introducing SSC-based LiDAR profiles, this study provides insights into the improvement of boundary condition realism in microscale urban ventilation modelling and is helpful for the development of climate-adaptive planning strategies for high-density cities facing heat risks.