Heat Island Types

A brief definition of the main heat island types

Heat island: The presence of any area warmer than its surrounding landscape. They can be developed on urban or rural areas. As it would be expected, there is a relatively minor knowledge about non urban heat islands, since they usually do not represent a risk for the human being or the environment. Meanwhile, urban heat islands have been profusely addressed during decades in urban areas with a wide range of climates and landscapes.

Urban heat island effect: The well-known phenomenon allusive to the atmospheric temperature rise experienced by any urbanized area. The heat island phenomenon has been commonly associated to cities, because their surfaces are characterized by low albedo, high impermeability and favourable thermal properties for the energy storage and heat release. Besides, many cities present narrow urban canyons with reduced sky view factors that tend to absorb and reemit the radiated energy from their surfaces. These factors contribute to urbanised areas increasing their temperatures in relation to their rural peripheries that are usually more vegetated, and therefore moderate the temperatures mainly through the evapotranspiration process, shades production and solar radiation interception.

Surface urban heat island: The remotely sensed urban heat island. It is observed by using thermal infrared data that allow to retrieve land surface temperatures. Usually, close relationships between the near surface air temperatures and land surface temperatures have been found. Therefore, the surface urban heat island is a reliable indicator of the atmospheric urban heat island.

Micro urban heat islands: They refer to urban hot spots as poorly vegetated parking lots, non-reflective roofs and asphalt roads. Micro urban heat islands are strongly affected by micro climate factors, therefore remotely sensed data are more suitable than atmospheric data for identifying heat spots.

Urban heat sink: Also called negative heat island. It is the expression of a city colder than their countrysides. There are few references about this phenomenon. Heat sinks have been observed in cities with temperate, tropical, semi-arid and arid climates, and mainly during the mornings (more information about this topic can be found in Peña (2008) and Peña (2009), see the "Bibliography" section of this website).