Satellite-Based Analysis of Urban Heat Island Dynamics under Extreme Heatwave Conditions and Mitigation Strategies in Thessaloniki

Heatwaves are among the most impactful and rapidly intensifying climate extremes in the Mediterranean region, where rising mean temperatures and the increasing frequency of extreme events interact with urban environments, exacerbating thermal stress. In densely populated cities, the Urban Heat Island (UHI) effect acts as a local amplification mechanism, transforming large-scale atmospheric heatwaves into compound extreme events with significant societal and environmental consequences. This study analyzes the spatial distribution and main controlling factors of extreme surface temperatures during three intense summer heatwaves in Thessaloniki, Greece, with the aim of linking observed geophysical extremes to urban configuration and assessing the potential of mitigation measures. For this aim, we employ LANDSAT 8–9 satellite imagery processed in QGIS to derive high spatial resolution Land Surface Temperature (LST) fields, together with key land-cover indicators such as the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Built-up Index (NDBI). These remote-sensing products are integrated with urban morphology and land-use data derived from OpenStreetMap (OSM), enabling a detailed characterization of how vegetation cover, building density, and surface materials modulate the urban thermal response under conditions of extreme atmospheric forcing. The results reveal pronounced spatial heterogeneity in LST across the metropolitan area, with persistent hotspots associated with compact historic districts, industrial zones, and highly impervious surfaces. In contrast, urban parks, coastal areas, and neighborhoods with a higher fraction of vegetation exhibit significantly lower surface temperatures, highlighting the role of land–atmosphere interactions and surface energy balance feedbacks in shaping urban-scale thermal extremes. The inverse relationship between NDVI and LST, together with the positive relationship between NDBI and LST, indicates the strong sensitivity of urban surface temperatures to land-cover composition during heatwave conditions. By framing the UHI as an intrinsic component of compound heat extremes, this work bridges observational geophysical analysis with the assessment of urban impacts. We further explore the potential of targeted mitigation strategies, such as the large-scale implementation of green roofs and high-albedo pavements, demonstrating their ability to reduce extreme surface temperatures and to moderate thermal exposure. The findings emphasize the importance of integrating physically grounded, data-driven mitigation measures into standardized urban planning frameworks in order to enhance resilience to future thermal extremes. More broadly, the study contributes to the understanding of how local-scale processes interact with large-scale climate extremes, offering transferable insights for Mediterranean and European cities increasingly exposed to heatwave risk under climate change.