Glossário

Definição: "Urban heat islands are a result of the physical properties of buildings and other structures, and the emission of heat by human activities. They are most pronounced on clear, calm nights; their strength depends also on the background geography and climate, and there are often cool islands in parks and less-developed areas. The urban heat island is the elevation of air temperature within cities, and to a smaller extent within towns and villages, relative to the surrounding countryside. It is caused mainly by the retention of solar heat in the fabric of buildings and ground surfaces, and the obstruction and re-absorption of night-time outgoing longwave radiation by buildings which obstruct the sky view. Paved ground surfaces transport more solar heat downwards than soil; this heat is then available for release overnight. Reduced ventilation can hinder the dispersal of urban heat islands. An important contribution to some urban heat islands is the emission of heat by human activities such as transport, and by heating and air conditioning of buildings. Accelerated run-off of rainwater, along with reduced vegetation cover can reduce moisture availability in cities. This can enhance the urban heat island by reducing the fraction of solar energy converted into latent heat and increasing the fraction becoming sensible heat.[...]. Generally, the urban heat island is strongest at night in high-rise city centers, weaker in residential suburbs, and also reduced in parks, although exceptions to this have been reported."
Fonte: Parker, D. E. (2010). Urban heat island effects on estimates of observed climate change. Wiley Interdisciplinary Reviews: Climate Change, 1(1), 123-133.