How complex terrains reshape urban wind patterns and cooling effects: Evidence from a high-density weather observation network in Hangzhou Bay, China

• Terrain and urbanization jointly shape local wind systems and cooling patterns. • UHI intensity shifts wind onset by 1-2 hours in the Hangzhou Bay region. • Local winds may intensify UHI by cooling rural areas more than urban zones. • Careful station selection is vital for estimating UHI in mountainous regions. Understanding how complex terrain influences urban wind patterns and cooling effects is crucial for addressing urban heat island (UHI) impacts and promoting climate-resilient cities. This study explores how terrain and urbanization jointly shape local wind systems and cooling in the Hangzhou Bay area, China, utilizing observational data from up to 574 meteorological stations (July–September, 2017–2021). Mixed local circulations occur 29–57% of the time. In this region, strong UHI intensity can advance or delay local wind onset by 1–2 hours and modify wind direction transitions, with clear west–east contrasts linked to the area's specific terrain—mountains to the west, sea to the east. These findings reflect localized interactions rather than universal patterns. Nocturnal mountain winds contribute over 2.5°C·h of cooling, especially from 17:00 to 19:00, with effects lasting ∼9 hours—significantly stronger than those of daytime sea breezes. However, these winds may intensify UHI effects by disproportionately cooling rural over urban areas. The results highlight the importance of region-specific station selection when assessing UHI, to avoid misinterpretations driven by local wind influences. This work provides actionable insights for improving urban ventilation and thermal comfort in complex terrain settings.