Urban heat Islands
The temperature in urban area is higher than the surrounding lesser urbanised area. This leads to formation of an island of heat (urban area) in sea of cooler region (surrounding lesser urbanised area).
|source: EPA 2008, www.urbanheatislands.com|
Why is heat island formed?
When an area gets urbanised the normal cover of vegetation is replaced by human built constructions. The human built constructions absorb and retain greater heat than the normal vegetation which earlier covered that area. This leads to rise in temperature. The human constructions/buildings cool off slowly, as a result the night temperature of urban area remains very much higher than surroundings.
- The vehicles emitting heat trapping gases.
- Increased release of body heat due to higher population. (minor)
- Disappearance of water bodies as they get covered during urbanisation.
Impact of Urban Island
The incoming air may rise up rapidly and can lead to higher precipitation.
The heat island may lead to formation of outgoing air waves which repeal incoming moisture laden air leading to lower precipitation.
In short, the precipitation pattern is affected and it becomes irregular.
The high heat in urban area increases cooling needs leading to higher consumption of energy as more air conditioners, fans will be operated. The increased energy needs will in turn cause pollution as more fossil fuels will be utilized in power plants for meeting the energy needs.
Human health and well being is adversely affected. The higher night temperature causes discomfort leading to reduction of sleep. The high temperature in most cities leads to irritation and dissatisfaction.