Abstract

The urban heat island (UHI) represents the relative warmth of urban areas compared to their nonurbanized surroundings. It can be observed in surface, air, and subsurface temperatures. The UHI arises because of changes to surface and atmospheric characteristics in cities that affect the surface energy budget. Urban surface cover, structure and material properties along with human energy and water use are important controls on the surface energy budget and therefore the UHI. The magnitude of the UHI is limited by weather conditions, especially wind and cloud cover as well as time of day and season. The geographical setting of the city also affects the temporal and spatial characteristics of the UHI. UHIs can impact human health and comfort, energy and water consumption, growing season length and biological processes, and can affect the weather over and downwind of cities. The UHI represents an unintentional change to climate at the scale of a city. Efforts to alter urban temperatures through application of “cool technologies” have shown promise and can help reduce the negative impacts of warmer urban temperatures associated with both the UHI and from large-scale climate change.