UHIs

An urban heat island (UHI) is a metropolitan area that experiences higher temperatures than surrounding rural areas, especially at night. The effect results from land cover changes (vegetation replaced by buildings and pavement), reduced evapotranspiration, heat storage in materials, and anthropogenic heat from vehicles and industry. Dark surfaces such as asphalt absorb solar radiation and release heat slowly, and tall buildings can trap heat in street canyons.

Impact and extent: UHIs are common in densely developed cities and can intensify during heat waves. City–rural temperature differences typically range from 1 to 3°C, with larger gaps possible in hot, dry climates. Consequences include higher cooling demand, poorer air quality, increased heat-related illness, and altered local wind and moisture patterns.

Mitigation: Strategies include increasing surface albedo (cool roofs and pavements), expanding urban green space (trees, parks, green roofs), water features, and porous surfaces. Urban design can improve shading and ventilation, while policy tools such as heat-health plans, building codes, and incentives support lower-heat cooling. District cooling and energy-efficient buildings also reduce local heat release.

Measurement and research: UHI intensity is the temperature difference between urban and rural areas, measured with weather stations or satellite data on land surface temperature. UHIs interact with broader climate change, potentially increasing heat exposure in cities and affecting rainfall and local weather. Understanding UHIs supports urban resilience and climate adaptation planning.