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The Heat Island Effect

The Heat Island Effect. Temperature distribution for Atlanta (from EPA). Review of last lecture. General circulation models: Grid size. 3 usages. Name of the basic set of equations. 4 components of the climate system model. Mesoscale models: grid size. 3 characteristics.

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The Heat Island Effect

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  1. The Heat Island Effect Temperature distribution for Atlanta (from EPA)

  2. Review of last lecture • General circulation models: Grid size. 3 usages. Name of the basic set of equations. • 4 components of the climate system model. • Mesoscale models: grid size. 3 characteristics.

  3. How do human activities change the global climate? Human beings are changing the global climate system in three different ways: • Change land cover (deforestation and afforestation) • Release or cleanse pollutants (aerosols) • Release or cleanse greenhouse gases

  4. Change of land cover

  5. Desertification • Caused mainly be human activities and climate change • Is one of the most significant global environmental problems • About a billion people are under threat

  6. Global desertification vulnerability

  7. Change of PSDI in the last 100 years

  8. Effects of vegetation • Makes water/heat reservoir deeper (transport deep water • out of soil) • Enhances evaporation (leafs increase evaporation area) • Dependent on vegetation type

  9. Global distribution of different vegetation types (From Bonon et al. 2002)

  10. Vegetation feedbackVegetation in turn is affected by environmental conditions (e.g. seasons, droughts, global warming)

  11. Effects of different surface types Convective instability increases Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Enhanced latent heat flux

  12. Video: Urban heat island effect (by Weather Channel) • http://www.youtube.com/watch?v=t-sXHl3l-rM

  13. The heat island effect • Nighttime: City warmer than surrounding rural area • Daytime: City has same air temperature as rural area

  14. Temperature distribution for Atlanta (from EPA)

  15. Dependence of heat island effect on population

  16. Causes of the heat island effect “Canyons” between buildings • Increased SW absorption caused by canyon geometry (increased area and multiple reflection) • Decreased LW loss caused by canyon geometry • Increased greenhouse effect caused by air pollution • Anthropogenic heat source • Increased sensible heat storage caused by construction materials • Decreased latent heat flux caused by change of surface type • Decreased sensible and latent heat fluxes caused by canyon geometry (reduction of wind speed)

  17. Mitigation of heat island effect • Greening the city (streets and roof top) • Change construction materials • Reduce anthropogenic heat sources

  18. Detection of Climate Change? • We must contend with the problem of enhanced urban heat islands influencing the data, which means that records from large urban areas are not representative of the surrounding region. • Atmospheric scientists are well aware of this source of bias in temperature records—which happens to be relatively small— and routinely account for its effect, either by discarding contaminated data or by adjusting values downward for affected stations.

  19. Summary • Effects of vegetation: (1) makes heat/water reservoir deeper, (2) enhance evaporation, (3) grows and dies in response to environmental conditions • Effects of different surface types: desert, city, grassland, forest, sea. Deeper heat/water reservoir and enhanced convective instability. • Heat island effect. 7 causes

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