Urban heatwaves reverse vulnerability-resilience relationships throughout the day

Abstract Urban resilience and vulnerability are often paired conceptually, but the dynamics of their relationships are rarely tested with space-time-based data. We tracked the 2019 European heatwave across Amsterdam, Rotterdam, and The Hague, combining hour-by-hour ambulance calls with district profiles identified from demographic, socioeconomic, health, and built environment attributes. We find significant differences in the factors driving vulnerability. The familiar rule of ‘more vulnerable, less resilient’ only partially holds: some vulnerable districts showed high resilience at particular times of the day, while seemingly less vulnerable districts showed low resilience. These swings point to the importance of local adaptive behaviours and urban social fabric in shaping dynamic vulnerability-resilience relationships. Our findings call for dynamic, district-specific planning: vulnerability assessments must look beyond averages, and resilience measures should flex with daily rhythms. Effective heatwave policy demands context-aware tools that treat resilience and vulnerability as intertwined, shifting properties of the urban social fabric.