Extreme heat becomes especially dangerous when high daytime temperatures continue through the night, leaving people and buildings little opportunity to cool. Dense urban form, heat-absorbing surfaces, limited vegetation, and poorly ventilated housing can intensify exposure.
Buildings, roads, and paved surfaces absorb heat during the day and release it slowly after sunset. Climate change is increasing the frequency, duration, and intensity of hot conditions, while urban design determines where shade, ventilation, green space, and cooler indoor environments are available.
Heat stress can worsen cardiovascular, respiratory, kidney, mental-health, and other medical conditions. It can disturb sleep, reduce the safety and productivity of outdoor work, increase electricity and water demand, and place pressure on hospitals and power systems. Older adults, young children, outdoor workers, and people without adequate cooling face particularly high risks.
Effective action combines heat-health warnings, heat action plans, public information, cooling centres, healthcare preparedness, and protection for outdoor workers. Longer-term measures include shade trees, accessible green space, cool roofs, reflective materials, passive ventilation, housing retrofits, and neighbourhood investment targeted toward the most exposed populations.
