Theory

• The temperature range from rural fringe to city centre is often greatest at night due to the high heat storage capacity of building materials compared to vegetation.
• Air over water is often relatively cool; a combination of the absorbtion of heat by the water itself and the evaporation at its surface, lowers the temperature.
• Why do cities tend to be warmer than rural areas?


  • City materials tend to be less reflective and thus, have a lower albedo e.g. concrete, bricks, tarmac (absorbs heat in the day, releases it at night)
  • Air pollution increases and creates a 'pollution dome,' allowing in short-wave radiation and absorbing outgoing radiation
  • Urban areas dispose of surface water quickly and has reduced vegetation - less evapotranspiration cooling
• Why is the urban heat island a matter of concern?

  • Rising temperatures can become uncomfortable in buildings and transport systems and can lead to heat stroke and even a death increase e.g. Paris 2019, 42.6 degrees celsius, 1435 deaths
  • Increased water consumption
  • Strains supply of energy for cooling and air conditioning
  • Anticyclonic weather conditions produce higher air pollution levels
  • Early pollen season (hay fever)
  • Climate change expected to increase urban heat island effect
• What is a cool roof made from?

  Materials with a high albedo
• How do cool roofs help manage urban heat islands?

  They absorb less heat during the day
• What is the benefit of green roads in urban areas?

  They allow water to seep in
• How much do green roofs reduce rooftop temperatures?

  20-40 degrees Celsius
• What additional benefit do green roofs provide besides temperature reduction?

  They provide habitat
• What is urban greening?

  Planting trees and vegetation in cities
• How does planting trees help manage urban heat islands?

  It provides shade and cools temperatures
• What does the sky view factor refer to?

  Openness between buildings in urban areas
• How does the sky view factor help reduce heat?

  It ventilates and reduces heat in urban areas
• What color cars absorb less heat?

  Light colored cars
• How do light colored cars help with urban heat management?

  They reduce the need for air conditioning
• What are the strategies for managing urban heat islands?

  • Cool surfaces: cool roofs with high albedo
  • Green roads: porous surfaces for water seepage
  • Green roofs: reduce rooftop temperatures by 20-40°C and provide habitat
  • Urban greening: planting trees and vegetation for shade
  • Sky view factor: openness for ventilation and heat reduction
  • Cool cars: light colored cars reduce heat absorption
• Urban and suburban areas experience higher temperatures than the surrounding rural areas and this difference is what constitutes an urban heat island. The annual mean air temperature of a city with one million or more people can be 1-3 degrees celsius warmer than its surroundings, but fluctuates throughout the year. Smaller urban areas will produce urban heat islands, but the effect tends to decrease as city size decreases.