Quantifying daily mismatch in urban cooling supply and demand at daytime and nighttime

• Analyse daily urban cooling mismatch at both daytime and nighttime. • Heat exposure varies spatially and temporally, even in stable climates. • Daytime heat exposure is more severe and persistent than nighttime exposure. • Densely built areas face greater heat exposure. Urban green-blue infrastructure (UGBI) has been identified as a sustainable strategy for urban heat mitigation. However, most studies assessing mismatches between cooling supply and demand use coarse temporal scales, thus overlooking temporal dynamics. Specifically, they ignore variability in weather conditions, land cover, and population distribution, as well as the different cooling mechanisms at daytime and nighttime. Here, we quantify daily supply and demand for urban cooling at daytime and nighttime, for the city of Can Tho, Vietnam. We used a biophysical model to derive city-wide daytime and nighttime temperatures as cooling supply, applied heat stress thresholds to assess daytime and nighttime cooling demand, and then calculated mismatches between supply and demand to generate potential heat stress maps. These maps were overlaid with daytime and nighttime population to evaluate heat stress exposure across the study area. Results show that in 2023, more than 90% of the population experienced daytime heat stress on 293 days, compared to only 100 days at night, primarily in April and May. Temporally, nighttime exposure is less constant, particularly in low-density built-up areas. These results demonstrate how integrating daily resolution and explicit day-night dynamics provides more detailed insights into urban cooling mismatches. Consistently, our findings highlight the need for spatially and temporally explicit UGBI planning strategies to strengthen urban resilience against heat stress.