Question:
Describe the causes of the phenomenon of 'urban heat island'. What are the effective measures to deal with this phenomenon in India?
(UPSC 2025, Paper 2, Geography Optional PYQ)
Answer.
Urban Heat Island (UHI) is a climatic phenomenon in which urban areas experience higher temperatures than surrounding rural areas due to human activities and built-up surfaces.
In scientific terms, the Urban Heat Island (UHI) intensity is measured as the difference between urban land surface temperature (LST) and nearby rural temperature.
Rapid urbanisation, concretisation, and reduction of vegetation have made Urban Heat Island (UHI) a major environmental issue in Indian cities.
We came to know by satellite data that land-surface temperatures increase with the expansion of built-up areas and the decline of vegetation cover.
Pattern and Spatial Distribution of Urban Heat Island in India:
The following are the spatial distributions:
1. Concentration in Large Metropolitan Cities:
The UHI effect is most prominent in densely built metropolitan regions such as:
- Delhi
- Mumbai
- Kolkata
- Chennai
- Hyderabad
- Bengaluru
- Ahmedabad
Satellite observations show that Delhi recorded one of the highest increases in nighttime land-surface temperature (about 2.02 °C between 2000 and 2023) among major cities.
2. Inland vs Coastal Cities
Inland cities (Delhi, Ahmedabad, Jaipur, Lucknow) show stronger UHI intensity due to continental climate and lack of maritime moderation.
Coastal cities (Mumbai, Chennai, Kolkata) have moderate UHI because sea breeze and water bodies help regulate temperature.
3. Urban Core vs Urban Fringe Pattern:
Typical spatial pattern:
- Central Business District: Highest temperature
- High-density residential areas: Moderate UHI
- Urban fringe: Transitional temperature
- Rural areas: Lowest temperature
4. Emerging Pattern in Tier-2 Cities
Rapidly expanding cities like Lucknow, Surat, Pune, and Guwahati are showing growing UHI intensity due to urban sprawl and land-use change.
Causes of Urban Heat Island:
The following are the major causes:
1. Replacement of Natural Land Cover
Urbanisation replaces vegetation and soil with concrete surfaces, which absorb and retain heat.
2. High Heat Absorption of Building Materials
Materials like cement, asphalt, and metal roofs have:
- High heat capacity
- Low albedo (reflectivity)
These surfaces store heat during the day and release it slowly at night, increasing nighttime temperatures.
3. Reduced Vegetation and Evapotranspiration
Trees cool the environment through evapotranspiration and shading.
Loss of green spaces in cities reduces this natural cooling mechanism.
4. Anthropogenic Heat Release
Human activities generate heat through:
- Vehicles
- Air conditioners
- Industrial processes
- Power plants
- This additional heat energy intensifies urban warming.
5. Urban Geometry and Heat Trapping
High-rise buildings create urban canyons that:
- Trap heat radiation
- Reduce wind circulation
- Increase thermal retention
6. Air Pollution and Greenhouse Effect
Pollutants and particulate matter absorb outgoing radiation and trap heat within urban atmospheres, enhancing the UHI effect.
Impacts of Urban Heat Island:
The following are consequences or impacts of Urban Heat Island:
- Increased heat-wave vulnerability in cities
- Higher electricity demand for cooling
- Health risks such as heat stroke and cardiovascular stress
- Increased air pollution and ozone formation
- Alteration of urban rainfall patterns
- Indian cities are warming faster than surrounding rural areas due to rapid urbanisation and energy consumption.
Effective Measures to Deal with UHI:
The following are ways forward to deal with Urban Heat Island:
1. Urban Greening and Afforestation:
Increase urban forests, parks, and green corridors
Promote street tree plantation
Develop green belts around cities
2. Green Roofs and Vertical Gardens
Vegetated roofs reduce surface temperature and improve building insulation.
3. Cool Roof and Reflective Materials
Use high-albedo materials such as:
- White reflective paint
- Cool pavements
- Solar reflective roofing
India has already started Cool Roof initiatives in cities like Ahmedabad and Hyderabad.
4. Protection of Urban Water Bodies
Restoration of:
- Lakes
- Wetlands
- Rivers
Water bodies help reduce local temperatures through evaporative cooling.
5. Sustainable Urban Planning
- Compact city design
- Mixed land use
- Transit-oriented development
- Adequate open spaces
6. Heat Action Plans (HAPs)
Cities such as Ahmedabad, Nagpur, and Delhi have introduced Heat Action Plans that include:
- Heat early-warning systems
- Cooling centres
- Public awareness campaigns.
7. Smart Climate-Resilient Infrastructure
Use of GIS, satellite monitoring, and AI-based heat mapping helps identify vulnerable neighbourhoods and plan mitigation strategies.
Urban Heat Island is an emerging urban climatic hazard in India, driven by rapid urbanisation, declining vegetation, and anthropogenic heat emissions. Its intensity is highest in large inland metropolitan areas, with the urban core significantly warmer than surrounding rural regions.
Addressing Urban Heat Island requires integrated urban planning, expansion of green infrastructure, cool roofing technologies, and climate-sensitive city design.
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