The Thermal and Rainwater Runoff Performance of an Extensive ...

The urban heat island effect describes the phenomena of higher average temperatures inurban areas compared with surrounding rural areas. This can lead to an increase in air-bornpollution and an increased use of air conditioning.Figure 14: Example of Urban Heat Island Effect [18]A number of complex factors contribute to the urban heat island effect. These include [19]:• Reduction of evaporating surfaces – more energy turned into sensible heat andless into latent heat• Thermal properties of materials – increased storage of sensible heat in buildingfabric• Anthropogenic heat released – from combustion of fuels and metabolism ofanimals/people• Canyon radiative effect – decrease of long-wave radiation lost to the sky andretained in the urban area due to radiation interchange between especially tallbuildings within relatively narrow streets and reduction of albedo due to multiplereflection of short-wave radiation between building surfacesNiall Carroll Page 33The Thermal and Rainwater Runoff Performance of an Extensive Green Roof System