Page 61 - GRIHA Manual Volume II - Introduction to National Rating System
P. 61
Sustainable site planning 53
CRIteRIon 5
ReduCe HARd pAvInG on-SIte
And/oR pRovIde SHAded
HARd-pAved SuRfACeS
Introduction
Dense urban city centres tend to have higher ambient temperatures than the surrounding sub-
urban rural areas. This phenomenon is known as the urban heat island effect (UHIE). The difference
in the ambient temperature could be in the order of 2°–6° C. The impact of UHIE is felt most during
summer months, especially during night.
Principal areas in the urban environment that lead to UHIE are parking lots, roads, building
facades and roofs, streets, and sidewalks.
Micro urban heat islands are heat islands that exist in dark, unshaded parking lots, roads,
unreflective long roofs, and so on.
The root cause of UHIE is the change in the energy balance of a given area caused due to human
interventions at various scales. Causes of UHIE range from urban setting and geometry to lack of
dense vegetation to surface finishes in individual buildings to anthropogenic heat generation from
various sources like transportation, industry, and air conditioning.
Urban heat islands are caused primarily (at the individual building scale) due to replacement of
vegetation and pervious surfaces with impervious surfaces constituted of dark coloured materials
like asphalt and concrete. This impacts the local ambient thermal balance of the urban environment
in two ways.
1. Evaporation deficit in the urban centres: Trees absorb heat through a process of evapo-
transpiration, thereby reducing ambient temperature of the surrounding environment. Pervious
paving and surfaces absorb water and allow it to evaporate, thereby reducing the temperature
of the surrounding environment. Cutting down of trees to make way for buildings and replacing
pervious surfaces with impervious surfaces does not allow for any evaporation to take place in
the urban areas. This means that the heat absorbed by these areas is unable to escape into the
atmosphere. This leads to rise in temperatures.
2. Thermal properties of the surface materials: Vegetative cover and trees tend to absorb less heat
and retain even lesser. On the other hand, dark coloured surfaces and materials like concrete,
steel, and asphalt, tend to absorb a substantial amount of heat. Due to their thermal storage
properties and reduced access to sky, they retain heat for a longer period of time and are unable
to lose this heat back into the atmosphere quickly.
There are various detrimental impacts of UHIE on the environment at both the macro as well as
the micro scale.
CRIteRIon 5
ReduCe HARd pAvInG on-SIte
And/oR pRovIde SHAded
HARd-pAved SuRfACeS
Introduction
Dense urban city centres tend to have higher ambient temperatures than the surrounding sub-
urban rural areas. This phenomenon is known as the urban heat island effect (UHIE). The difference
in the ambient temperature could be in the order of 2°–6° C. The impact of UHIE is felt most during
summer months, especially during night.
Principal areas in the urban environment that lead to UHIE are parking lots, roads, building
facades and roofs, streets, and sidewalks.
Micro urban heat islands are heat islands that exist in dark, unshaded parking lots, roads,
unreflective long roofs, and so on.
The root cause of UHIE is the change in the energy balance of a given area caused due to human
interventions at various scales. Causes of UHIE range from urban setting and geometry to lack of
dense vegetation to surface finishes in individual buildings to anthropogenic heat generation from
various sources like transportation, industry, and air conditioning.
Urban heat islands are caused primarily (at the individual building scale) due to replacement of
vegetation and pervious surfaces with impervious surfaces constituted of dark coloured materials
like asphalt and concrete. This impacts the local ambient thermal balance of the urban environment
in two ways.
1. Evaporation deficit in the urban centres: Trees absorb heat through a process of evapo-
transpiration, thereby reducing ambient temperature of the surrounding environment. Pervious
paving and surfaces absorb water and allow it to evaporate, thereby reducing the temperature
of the surrounding environment. Cutting down of trees to make way for buildings and replacing
pervious surfaces with impervious surfaces does not allow for any evaporation to take place in
the urban areas. This means that the heat absorbed by these areas is unable to escape into the
atmosphere. This leads to rise in temperatures.
2. Thermal properties of the surface materials: Vegetative cover and trees tend to absorb less heat
and retain even lesser. On the other hand, dark coloured surfaces and materials like concrete,
steel, and asphalt, tend to absorb a substantial amount of heat. Due to their thermal storage
properties and reduced access to sky, they retain heat for a longer period of time and are unable
to lose this heat back into the atmosphere quickly.
There are various detrimental impacts of UHIE on the environment at both the macro as well as
the micro scale.
