Building urban climate resilience through high-resolution UAV thermography: Lessons from Coimbra (Portugal)

Source abstract

Fine-scale thermal dynamics in medium-sized cities remain underexplored despite growing evidence of urban overheating. This study examines neighbourhood-scale surface thermal patterns and their coupling with near-surface air temperature in Coimbra, Portugal, using high-resolution unmanned aerial vehicle (UAV) thermal infrared remote sensing combined with synchronised in situ microclimatic measurements. Thermal imagery was acquired on a clear summer afternoon at sub-metre resolution (∼0.10–0.20 m), mapping land surface temperature (Ts) across three contrasting sectors: a dense historic corridor, a mixed recreational area, and a continuous green–blue riverfront corridor. UAV-derived Ts data were synchronised with air temperature (Ta) measurements at pedestrian height. Results reveal pronounced spatial heterogeneity, with Ts differences exceeding 20 °C over short distances and maximum values above 50 °C on exposed impervious and synthetic surfaces. Vegetated and river-adjacent areas were 10–15 °C cooler than dense built-up zones. A strong overall Ts–Ta relationship was observed (R 2 = 0.67), but coupling was substantially attenuated in the vegetated riverfront sector (R 2 = 0.54; slope = 0.26) due to shading, evapotranspiration, and modified energy partitioning. These findings show that medium-sized cities can display thermal contrasts comparable to larger metropolitan areas and highlight the role of continuous green–blue infrastructure in moderating urban thermal conditions. The study demonstrates the value of UAV thermography for resolving microclimatic variability at pedestrian scales. Urban planners and municipal authorities should prioritise the preservation, expansion, and connectivity of green–blue corridors as a cost-effective approach to reducing surface heat exposure and improving thermal resilience. • UAV thermography reveals >20 °C surface contrasts within a medium-sized city. • A continuous green–blue corridor is 10–15 °C cooler than dense built-up areas. • Surface–air coupling (R 2 = 0.67) weakens in vegetated, well-watered sectors. • Sub-metre UAV imagery resolves microclimates beyond satellite reach. • Synthetic turf exceeded 50 °C, signalling a thermal risk in recreational areas.