Cities often feel noticeably hotter than the surrounding countryside, a phenomenon known as the urban heat island (UHI). An urban heat island is a metropolitan area that becomes significantly warmer than nearby rural regions, largely because concrete, asphalt, and buildings absorb and retain heat. In such environments, waste heat, generated by cars, public transport, factories, homes, and even people themselves, (1) ______. When buildings and paved surfaces are constructed close together, they trap heat, and this insulation effect, which slows the release of warmth, causes temperatures in the spaces between structures to remain high even after sunset.

At night, the contrasts becomes especially clear. Surfaces such as roads, sidewalks, and parking lots act like vast reservoirs of heat, preventing warmth from escaping into the cooler night sky. In a dense city core, skyscrapers and narrow streets restrict airflow, (2) ______. The consequences are serious: poorer air quality develops because pollutants released by vehicles and industry cannot disperse easily, while local water systems are harmed when heated runoff enters streams and rivers, damaging aquatic species adapted to cooler conditions. Urban heat islands also place a heavy strain on energy networks, since residents increasingly rely on air conditioning during summer peaks, (3) ______.

To reduce these effects, urban planners, policymakers, and architects are developing both modest and ambitious strategies. Green roofs, essentially gardens on rooftops, help cool buildings by absorbing sunlight and converting it into biomass rather than heat. (4) ______. Expanding urban vegetation and creating more open layouts improve air circulation, allowing heat to dissipate. Though urban heat islands represent a modern challenge, thoughtful design and collective action can lessen their impact, (5) ______.
(Adapted from https://education.nationalgeographic.org)