(a) Bring out the causes for the formation of heat islands in the urban habitat of the world. (b) What do you understand by the phenomenon of ‘temperature inversion’ in meteorology? How does it affect weather and the habitants of the place?

(a) Causes of urban heat islands

An urban heat island (UHI) is the dome of higher temperatures over a city compared with its rural surroundings, most marked on calm, clear nights.

• Concrete, asphalt and dark roofs have low albedo and high heat capacity: they absorb solar radiation by day and release it slowly at night.
• Loss of vegetation and wetlands cuts evapotranspiration, removing natural cooling.
• Anthropogenic heat from vehicles, industries and air-conditioning adds directly to the urban energy budget.
• Urban canyon geometry of tall buildings traps outgoing long-wave radiation through multiple reflections and reduces ventilation.
• The pollution dome of aerosols and greenhouse gases re-radiates heat back to the surface, while impervious surfaces shed rainwater quickly, keeping the city dry and hot.

(b) Temperature inversion and its effects

Temperature inversion is the reversal of the normal lapse rate — temperature increases with altitude in a layer. It develops through nocturnal radiational cooling on calm clear nights, cold-air drainage into valleys, subsidence in anticyclones, and along fronts.

• Weather effects: the inversion layer is highly stable, suppressing convection, cloud growth and rainfall; it favours fog, mist and frost.
• Effects on inhabitants: pollutants and smoke get trapped below the inversion lid, producing smog episodes (Delhi winters, the 1952 London smog); valley frost damages crops, so orchards and vineyards, as well as settlements, occupy the warmer thermal belts on slopes; fog disrupts transport and aviation.

Both phenomena show how energy-budget changes translate directly into human discomfort and hazard.