Answer Synopsis 26/11/2020

Question : Define Urban Heat Island effect? Enlist and describe the causes and effect of urban heat island effect?


Urban Heat Island effect is defined as the presence of significantly higher temperatures in urban areas compared to the temperatures in surrounding rural zones mainly due to human factors. Usually urban heat islands have a mean temperature 8 to 10 degrees more than the surrounding rural areas

Causes of Urban Heat Island effect

  1. Use of construction materials like Asphalt and concrete: Asphalt and concrete, needed for the expansion of cities, absorb huge amounts of heat, increasing the mean surface temperatures of urban areas.
  2. Dark surfaces: Many buildings found in urban areas have dark surfaces, thereby decreasing albedo and increased absorption of heat.
  3. Air conditioning: Buildings with dark surfaces heat up more rapidly and require more cooling from air conditioning, which requires more energy from power plants, which causes more pollution. Also air conditioners exchange heat with atmospheric air, causing further local heating. Thus there is a cascade effect that contributes to the expansion of urban heat islands.
  4. Urban Architecture: Tall buildings, and often, accompanying narrow streets, hinder the circulation of air, reduce the wind speed, and thus reduce any natural cooling effects. This is called the Urban Canyon Effect.
  5. Need for mass transportation system: Transportation systems and the unimpeded use of fossil fuels also add warmth to urban areas.
  6. Lack of Trees and green areas: which impedes evapotranspiration, shade and removal of carbon dioxide, all the processes that help to cool the surrounding air.

After effects on a variety of forces and factors

  • Impact on animals:
  1. Urban heat islands will be prolonging the growing season, thus throwing the breeding strategies of the inhabiting species in disarray.
  2.  With the temperature of the nearby buildings sometimes reaching over 50 degrees and above precipitation will warm rapidly, causing runoff into nearby streams, lakes and rivers (or other bodies of water) to provide excessive thermal pollution.
  3. The increase in thermal pollution has the ability to increase water temperature by 20 to 30 degrees. This increase will cause the fish species inhabiting the body of water to undergo thermal stress and shock due to the rapid change in temperature to their climate.
  4. Urban heat islands caused by cities have altered the natural selection process. Selective pressures like the temporal variation in food and water are relaxed causing a new set of selective forces to roll out.
  • Impact on weather and climate:
  1. Aside from the effect on temperature, UHIs can produce secondary effects on local meteorology, including the altering of local wind patterns, the development of clouds and fog, the humidity, and the rates of precipitation.
  2. The extra heat provided by the UHI leads to greater upward motion, which can induce additional shower and thunderstorm activity.
  3. In addition, the UHI creates during the day a local low-pressure area where relatively moist air from its rural surroundings converges, possibly leading to more favourable conditions for cloud formation. Rainfall rates downwind of cities have increased between 48% and 116%. Partly as a result of this warming, monthly rainfall is about 28% greater between 20 miles (32 km) to 40 miles (64 km) downwind of cities, compared with upwind. Some cities show a total precipitation increase of 51%.

Therefore, considering the above-mentioned impact, it turns to be the need of the hour to counter them with apt strategies. To conclude, on a brief note, the increasing global warming needs anthropogenic intervention to make the earth habitable but these interventions should be fool proof.

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