Surface urban heat islands during heatwaves: Thermal impacts on the built environment in selected polish cities

• Inland cities like Wrocław and Kraków had UHI intensities up to 2°C. • Lower wind speeds during heatwaves worsened UHI effects, particularly inland. • Coastal cities like Gdańsk have milder UHI from cooling breezes, but these lessen during long heatwaves. • The study supports city-specific thermal mitigation strategies. This study investigates the relationship between synoptic weather patterns, heatwave events, Urban Heat Island (UHI) classification, and UHI intensities, where the term 'UHI' in this analysis specifically refers to the surface UHI effect. The focus is on Central and Eastern Europe during August 2020 and June 2021, a period that was important due to several significant heatwaves that occurred. It focuses on four major Polish cities, including Wrocław, Kraków, Poznań, and Gdańsk, using Sentinel-3 Sea and Land Surface Temperature Radiometer (SLSTR) images, synoptic station measurements, ERA5 data, and Weather Research and Forecasting (WRF) model outputs. The results show that long-lasting surface high-pressure systems over Central Europe were key drivers of prolonged heatwave conditions. Inland cities like Wrocław and Kraków experienced more intense UHI effects, with peak UHI intensities reaching up to 2°C, compared to coastal cities like Gdańsk, where the UHI intensity averaged 0.38°C. The study also explores the role of reduced wind speeds in amplifying UHI effects, showing that average wind speeds in inland cities dropped by about 0.50 m·s −1 during heatwaves, further exacerbating the UHI effects, especially in Wrocław and Kraków. Findings support the development of city-specific thermal mitigation strategies and enhance understanding of urban climate resilience under extreme weather conditions.