Urban Heat Island Effect

• 30 Apr 2025

Source: TH 

Why in News? 

A recent study highlights the dual impact of the Urban Heat Island (UHI) effect—while it elevates heat-related mortality, it substantially reduces cold-related deaths.  

• In 2018, the global decline in cold-related fatalities was 4.4 times greater than the rise in heat-related deaths, with cities like Moscow witnessing even larger differentials.
  

What is Urban Heat Island? 

• About: An Urban Heat Island (UHI) is a metropolitan area significantly warmer than nearby rural surroundings. 
  • Urban areas heat up more than natural landscapes because materials like concrete and asphalt absorb and retain heat more effectively. 
  • The effect is most noticeable in large, densely populated cities like New Delhi,  New York, Paris, and London. 

 

• Causes:  
  • Impervious Surfaces: Materials like asphalt, concrete, and steel absorb daytime heat and release it slowly at night due to low albedo, trapping more heat. 
  • Lack of Vegetation: Limited green cover and tree canopy reduce evapotranspiration, cutting off natural cooling and increasing urban heat buildup. 
  • Anthropogenic Heat: Vehicular emissions, industrial processes, and air conditioning release excess heat, significantly raising urban temperatures. 
  • Air Pollution and Soot: Black carbon and other particulate matter absorb solar radiation, raising ambient temperatures and worsening the UHI effect. 
  • Urban Morphology: Dense buildings, narrow streets, and poor airflow create an urban canyon effect, trapping heat within confined spaces. 
    • Skyscrapers and high-rises restrict air flow and trap heat. 

• Consequences: 
  • Increased Energy Demand: UHI raises cooling energy use, straining grids and increasing carbon emissions. 
    • By elevating local temperatures, urban areas drive up energy consumption for cooling and positioning urban heat islands as localized accelerators of climate change. 
  • Deterioration of Air Quality: Higher temperatures boost ground level ozone formation, worsening smog and respiratory issues. 
  • Heat-Related Health Risks: UHI increases heat strokes, dehydration, and cardiovascular stress, especially in vulnerable groups. 
  • Strain on Water Resources: UHI accelerates evaporation, reducing water availability and increasing cooling water demand. 
  • Biodiversity Loss: UHI harms native vegetation, disrupts ecosystems, and threatens urban wildlife due to excessive heat and reduced green spaces 
• UHI Mitigation Strategies: 

UHI Mitigation Case Studies: 

• Los Angeles Cool Roof Initiative: It requires the use of reflective roofing materials in all new buildings and major renovations to ensure roofs effectively reflect sunlight and release absorbed heat through high solar reflectance and thermal emittance. 
• Dubai’s Smart Cooling Systems: It involves generation of chilled water at a central facility and distributing it via underground pipes to multiple buildings leading to 30–50% more energy-efficient than individual AC units.  
• Paris’ Cool Streets Initiative: It is a comprehensive urban transformation program aimed at combating urban heat by: 
  • Converting streets into pedestrian-only zones. 
  • Replacing asphalt with plants and trees, thereby increasing green space in urban areas etc.

Click Here to Read More: Heat Waves 

UPSC Civil Services Examination, Previous Year Question (PYQ) 

Q. What are the possible limitations of India in mitigating global warming at present and in the immediate future? (2010)

1. Appropriate alternate technologies are not sufficiently available.
2. India cannot invest huge funds in research and development.
3. Many developed countries have already set up their polluting industries in India.

Which of the statements given above is/are correct?

(a) 1 and 2 only  

(b) 2 only 

(c) 1 and 3 only  

(d) 1, 2 and 3 

Ans: (a)