Why in News?
A study by researchers from University of East Anglia finds that Indian cities may experience much higher temperature rise than projected by global climate models due to the Urban Heat Island (UHI) effect.
Description:
Key Findings of the Study:
- Coverage: 104 medium-sized cities (tropical & sub-tropical); 18 Indian cities analysed in detail.
- Core Result: All Indian cities studied warm faster than surrounding rural areas.
- Magnitude: Indian cities show ~45% more warming than projected by ESMs for the broader region.
Urban Heat Island (UHI): Cities being hotter than nearby rural areas due to build surfaces, reduced vegetation, and waste heat.
Causes of UHI:
| Factor | Mechanism of Action |
| Low Albedo | Dark surfaces (asphalt/concrete) absorb more solar radiation. |
| Urban Geometry | Tall buildings create “Urban Canyons” that trap heat and block wind. |
| Vegetation Loss | Reduced evapotranspiration (natural cooling process). |
| Waste Heat | Heat from AC exhausts, vehicle engines, and industries. |
Key Characteristics:
- Diurnal Variation: UHI is typically strongest at night as buildings release stored heat.
- Seasonal Peak: More intense during heatwaves and dry summer months.
- Spatial Density: Directly proportional to the density of “grey infrastructure” (pavements/buildings).
Impact Matrix:
- Health: Increased incidence of heat exhaustion, strokes, and mortality (especially for outdoor workers).
- Economy/Energy: A “vicious cycle” where heat leads to more AC use, increasing peak power demand and emissions.
- Social Equity: Vulnerable populations in informal settlements (slums) face the highest thermal stress due to poor ventilation.
Mitigation Strategies:
| Strategy | Specific Measures |
| Cool Surfaces | White/Reflective roofs and light-colored pavements to increase albedo. |
| Blue-Green Infra | Restoring urban wetlands, lakes, & creating vertical gardens/urban forests. |
| Passive Design | Building “Ventilation Corridors” to allow natural airflow through the city. |
| Policy | Integration of UHI data into Heat Action Plans (HAPs) and building codes. |
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