Relevance: GS I (Urbanization) & GS III (Climate Change) | Source: The Hindu / PNAS Study
1. The Flaw: Models vs. Reality
A new study reveals a critical gap in our climate predictions. Standard Earth System Models (ESMs)—used by bodies like the IPCC—underestimate the future warming of Indian cities by approximately 45%.
- The Gap: While global models predict a temperature rise of 2.2°C, the actual rise in cities (when urban concrete/asphalt is accounted for) is likely to be 2.6°C – 2.7°C.
- The “Patiala Paradox”: The city of Patiala (Punjab) was identified as an extreme outlier. It is projected to warm at double the rate of its rural surroundings (potentially seeing a 4°C rise when models predict only 2°C).
2. The Physics: Why the Difference?
Global models often “blend” cities with the surrounding countryside. They miss two key local factors:
- Evapotranspiration Gap: In rural areas, plants release water vapor (sweating), which actively cools the air. Cities, covered in concrete, lack this natural cooling mechanism.
- Albedo Effect: Urban surfaces (dark roads, buildings) have low albedo (reflectivity), meaning they absorb more heat compared to crops or soil, trapping it locally.
3. The Implication: Policy Failure?
If cities are getting hotter than we think, our current Heat Action Plans (HAPs) might be insufficient.
- Wet-Bulb Danger: The threshold for fatal humidity-heat combinations may be breached sooner than expected in cities like Jalandhar and Patiala.
- Energy Spike: Higher local temperatures lead to a non-linear spike in electricity demand for ACs, threatening grid stability.
UPSC Value Box
| Concept / Term | Relevance for Prelims |
| Urban Heat Island (UHI) | A phenomenon where an urban area is significantly warmer than its surrounding rural areas due to human activities, concrete surfaces, and lack of vegetation. |
| Evapotranspiration | The sum of evaporation from the land surface plus transpiration from plants. It is a natural cooling process often missing in concrete-heavy cities. |
| Earth System Models (ESMs) | Complex computer simulations used to predict future climate. They simulate interactions between atmosphere, ocean, land, ice, and biosphere. |
Q. With reference to the phenomenon of “Urban Heat Islands” (UHI), consider the following statements:
- It refers to urban areas being significantly warmer than their surrounding rural areas.
- The presence of high albedo surfaces like dark asphalt roads helps in reducing the UHI effect.
- Reduced evapotranspiration in cities contributes to higher local temperatures compared to vegetated rural areas.
Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Correct Answer: (c)
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