UHI is the effect of negative impact that urbanization has on the environment. The technical definition of UHI is that it is a closed isotherms indicating an area of the surface that is relatively warm; most commonly associated with areas of human disturbance such as towns and cities. It is also defined as – An urban heat island (abbreviated as UHI) is where the temperature in a densely populated city is as much as 2 degrees higher than suburban or rural areas. This is a human induce effect as it is caused due to the increase in temperature from human activities. UHI can cause biophysical hazards such as heat stress, air pollution and other grave issues including heat related mortality, which are predicted to be a more important concern in the future. Urban heat islands can be a huge possible threat in the near mainly because they may contribute towards the alarmingly rising global warming of the present, even though this UHI phenomenon can have an effect only at a local area scale.
Urban heat islands are an
indirect result of increase in built structure which are constructed to
facilitate the human needs such as asphalt roads and concrete buildings, on the
earth’s surface. These material can absorb a great deal of heat which causes a
rise in overall temperature of the urban area. When the vegetation cover is
reduced to make room for infrastructure, the natural cooling effect of the
earth is affected, which also contributes towards the formation of urban heat
The composition of cities is a major factor that contributes to the formation of UHIs. If the city is packed with tall buildings and narrow streets which create very less room for urban open spaces, it may lead to heating of the air which is trapped between them. This can result increased warmth and reduced air flow in these areas since tall building is an obstruction to air circulation. Improper waste dumping and heat from vehicles can also add to the cause. Cities with almost no vegetation cover, also known as urban deserts like Abu Samra of Qatar, can increase the heat in the atmosphere. Urban deserts with built mass constructed with materials impermeable to rain can increase the surrounding temperature considerably.
The major impacts of heat islands on the people and surroundings include:
Landsat and Suomi-NPP are two Earth-observing satellites that can monitor the planet's vegetation and surface temperature. This data can be used by scientists to track UHI hotspots in cities all over the world. NASA scientists are using global satellite views to better understand urban heat islands and to assist urban planners in designing communities that are more energy efficient, cooler, and safer.