• A new study uses Barcelona as a reference city to show how night-time heat prolongs thermal stress, limits recovery and increases health risks during heatwaves.

• The study was conducted by researchers from the Earth Sciences Department at the Barcelona Supercomputing Center with contribution from the Universitat Autònoma de Barcelona.

Researchers from the Earth System Services (ESS) group of the Earth Sciences Department at the Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS), in collaboration with the Universitat Autònoma de Barcelona, conducted a new scientific study revealing that heat-related vulnerability often persists well into the night, even after daytime temperatures begin to fall. Using Barcelona as a reference city, the research shows how high minimum temperatures, limited nocturnal cooling and heat retention, particularly in dense urban environments, can extend exposure to thermal stress during heatwaves and reduce opportunities for physiological recovery. The study has been published as a short communication in the journal City and Environment Interactions.

By focusing on night-time conditions, the study challenges the common assumption that heat impacts subside after sunset. Instead, it highlights how prolonged exposure across the full day–night cycle can lead to cumulative health effects, increasing risks for vulnerable groups such as older adults, people with chronic conditions and residents of densely built neighbourhoods. The findings underline the need to integrate night-time heat indicators into climate risk assessments, early warning systems and adaptation planning. By accounting for the full temporal dynamics of heat exposure, the study supports more effective urban design, public health strategies and climate services aimed at reducing heat-related impacts in a warming climate, particularly in cities facing increasingly frequent and intense heatwaves.

Reference:

Hu, J.; Gignac, F.; Pickard, S.; Trascasa-Castro, P.; Duzenli, E. & Bojovic, D.; When the sun goes down, heat vulnerability remains; City and Environment Interactions; Volume 29, January 2026, 100284; https://doi.org/10.1016/j.cacint.2025.100284.